A radar system comprising two back-to-back positioned radar antenna modules, and a radar system holding an antenna module with cavity slotted-waveguide antenna arrays for radiating and receving radar wave signals

ABSTRACT

A radar system with antenna modules that have first and second planar slotted waveguide antenna arrays for radiating and receiving electromagnetic waves. A rotation system supports and rotates the antenna modules around a vertical axis, modules are arranged back-to-back on opposite sides of a plane intersecting the vertical axis of rotation. Another radar system includes planar slotted waveguide antenna arrays with longitudinal extending waveguide columns. The front side of the columns holding the cavity slots of the first planar antenna array are positioned in a first plane and the front side of the columns holding the cavity slots of the second planar antenna array are positioned in a second plane parallel to the first plane. The arrays may be positioned at a distance to each other in a direction to the first and second planes. The parallel planes may be offset with a minimum perpendicular array distance.

TECHNICAL FIELD

The disclosure relates to a radar system comprising two back-to-backpositioned radar antenna modules. The disclosure also relates to a radarsystem holding cavity slotted-waveguide antenna arrays for radiating andreceiving radar wave signals. The disclosure also relates to antennamodules with radiating and receiving antenna arrays positioned with adistance to each other.

BACKGROUND

In the prior art, slotted-waveguide antennas, SWA, are well-known, wherethe waveguides may be arranged in an array of waveguides, such as aplanar array of parallel waveguides. As the name suggests,slotted-waveguide antennas consist of lengths of waveguides with amultiple number of slots formed in the conducting walls of thewaveguides. These slots introduce discontinuities in the conductor andinterrupt the flow of current along the waveguide. Instead, the currentmust flow around the edges of the slots, causing them to act as dipoleantennas.

The two basic types of SWAs are standing wave and traveling waveantennas. In a traveling wave SWA, the waveguide is built with matchedloads or absorbers at the end, while in a standing wave SWA, the end ofthe waveguide is short-circuited.

Depending on the desired electric field polarization, the slots can beplaced on either the narrow or broad wall of the waveguide. At thefundamental TE10 mode, longitudinal slots on the broad wall will producea field with vertical polarization, while transverse slots on the narrowwall result in a horizontal field polarization.

For antenna systems used to detect small targets, such as birds orUnmanned Aerial Vehicles, UAV's, in a clutter rich environment, ahorizontal polarization is preferred, which can be obtained by using anarray of waveguides with transverse slots on the narrow wall.

Multi-beam radar systems with Frequency Modulated Continuous Wave, FMCW,waveforms is known in the art, and by using an antenna holding cavityslotted-waveguide arrays for transmitting and receiving electromagneticwaves, it is possible to obtain a multi-beam FMCW antenna system, whichis very compact in size, and which is suitable for detecting smalltargets, such as birds or UAV's.

When detecting small objects or targets, it is required to have a highsignal to noise ratio.

Noise may be introduced by having false reflections from the radiatingantenna reaching the receiving antenna.

It would be advantageous to have an improved cavity slotted-waveguideantenna system, which reduces false reflections from the radiatingantenna to the receiving antenna, thereby increasing the possibility ofa correct classification of detected objects or targets.

A higher signal to noise ratio may also be obtained by having anincreased radar signal exposure time on the object or target.

It would therefore be advantageous to have an improved cavityslotted-waveguide antenna system, which allows a high radar signalexposure time on an object or target, and which thereby increases thepossibility of a correct classification of detected objects or targets.

SUMMARY

The aspects of the disclosed embodiments are directed to provide acavity slotted-waveguide antenna array system, which allows a high radarsignal exposure time on an object or target.

According to a first aspect there is provided a radar system comprisinga first and a second antenna module, each said antenna modulecomprising:

a first planar slotted waveguide antenna array configured for radiatingelectromagnetic waves; and

a second planar slotted waveguide antenna array configured for receivingelectromagnetic waves;

wherein for each of the antenna modules, each planar slotted waveguideantenna array comprises several longitudinal extending waveguide columnsdisposed in a parallel and adjacent position with respect to oneanother, said waveguide columns having a front side and a rear side witha plurality of cavity slots on the front side, and said waveguidecolumns further having first and second column ends; and

wherein for each of the antenna modules, the first and second antennaarrays are arranged with the longitudinal direction of the waveguidecolumns extending in a single, horizontal direction, and with thewaveguide columns of the first antenna array disposed below and in aparallel position to the waveguide columns of the second antenna array;

said radar system further comprising a rotation system configured forsupporting and rotating the first and second antenna modules around avertical axis, with the first and second antenna modules arranged in aback-to-back position on opposite sides of a plane intersecting thevertical axis of rotation, and with the rear side of the waveguidecolumns of the antenna arrays of the first antenna module facing therear side of the waveguide columns of the antenna arrays of the secondantenna module.

Thus, the front side of the waveguide columns of the antenna arrays ofthe first antenna module faces away from the front side of the waveguidecolumns of the antenna arrays of the second antenna module. This allowsthe first and second antenna modules to transmit electromagnetic wavesin different directions. By having a rotating radar system with twoback-to-back positioned antenna modules, it is possible to decrease thespeed of rotation to half the speed of a rotating radar system, whichcomprises only a single radar module, while still having the same speedof update of radar tracks obtained from received signals being reflectedfrom detected objects or targets. By lowering the speed of rotation, ahigher signal exposure time on target is obtained, resulting in a highersignal to noise ratio, which again results in more information of anydetected target or object.

In a possible implementation form of the first aspect, the systemfurther comprises a protective housing in the form of a radome coveringsaid first and second antenna modules.

In a possible implementation form of the first aspect, the radome isarranged in a fixed position without following the rotation of therotation system and the antenna modules. It is also within analternative embodiment that the radome is connected to the rotationalsystem for being rotated by the rotation of the rotational system.

In a possible implementation form of the first aspect, the waveguidecolumns within the first and second antenna arrays of both the first andsecond antenna modules have equal dimensions or equal mechanicaldimensions. By having equal dimensioned waveguide columns for bothantenna modules, it is possible to operate within the same frequencyband for both antenna modules.

In a possible implementation form of the first aspect, then for one orboth of the antenna modules, the front side of the columns holding thecavity slots of both the first and second antenna arrays are positionedsubstantially in the same plane. By having the radiating and receivingarrays in the same plane, a simplified manufacture of the antenna modulemay be obtained.

In a possible implementation form of the first aspect, then for one orboth of the antenna modules, the cavity slots on the front side of thecolumns of the first array are arranged in a first plane, and the cavityslots on the front side of the columns of the second array are arrangedin a second plane, and the first and second arrays are positioned withan angle between said first plane and said second plane. This angleshould be a blunt or abuse angle, which may be closer to 180° than to90°. By having the radiating and receiving arrays in angled planes, ahigher scanning coverage may be obtained.

In a possible implementation form of the first aspect, the cavity slotson the front side of the columns of the second antenna array of thefirst antenna module are arranged in a partially upwards facing planehaving a first acute angle to the vertical direction, and the cavityslots on the front side of the columns of the first antenna array of thesecond module are arranged in a partially upwards facing plane having asecond acute angle to the vertical direction. In a possibleimplementation form of the first aspect, the first acute angle issubstantial equal to the second acute angle.

In a possible implementation form of the first aspect, the first andsecond acute angles are in the range of 10-30°, such as about 20°.

In a possible implementation form of the first aspect, the first andsecond antenna module are arranged in a mirrored position relative tosaid plane intersecting the vertical axis of rotation.

In a possible implementation form of the first aspect, the radome has adome shaped upper part. The dome shape gives an increased mechanicalstrength.

In a possible implementation form of the first aspect, the radome ismade of a material having a high electromagnetic transparency, such as aplastic material, such as a polyethylene (PE) or polypropylene (PP)based material, such as a polyethylene (PE) or polypropylene (PP) basedultra heigh molecular weight plastic material.

In a possible implementation form of the first aspect, the radome ismade of a material having a thickness in the range of 1-3mm, such as inthe range of 1-2 mm or such as in the range of 1-1.5 mm.

When having two back-to-back simultaneously operating antenna modules,it is important to minimize reflection of signals transmitted orradiated from the radiating array of one module to the receiving arrayof the other module. By reducing the material thickness of the radome,the electromagnetic transparency of the radome is increased, therebyminimizing the internal reflection from the radome. By using a PE or PPbased material, such as a PE or PP based ultra heigh molecular weightplastic material, the electromagnetic transparency of the radome isincreased even further.

In a possible implementation form of the first aspect, then for one orboth antenna modules, an electromagnetic shield or shield plate isarranged substantially parallel to the waveguide columns and between thefirst lower radiating antenna array and the second upper receivingantenna array, which shield or shield plate may extend outwards from thefront side of the antenna module.

In a possible implementation form of the first aspect, theelectromagnetic shield or shield plate is an electromagnetic absorbingshield or shield plate. The shield or shield plate may be fully or atleast partly covered by an electromagnetic absorbing material.

In a possible implementation form of the first aspect, then for one orboth antenna modules, a lower electromagnetic shield or shield plate,which may be an electromagnetic absorbing shield or shield plate, andwhich may be fully or at least partly covered by an electromagneticabsorbing material, is arranged substantially parallel to the waveguidecolumns and below the lowermost waveguide column of the first lowerradiating antenna array. The lower electromagnetic shield or shieldplate may extend outwards from the front side of the antenna module.

In a possible implementation form of the first aspect, then for one orboth antenna modules, an upper electromagnetic absorber shield or shieldplate, which may be an electromagnetic absorbing shield or shield plate,and which may be fully or at least partly covered by an electromagneticabsorbing material, is arranged substantially parallel to the waveguidecolumns and above the uppermost waveguide column of the second upperreceiving antenna array. The upper electromagnetic shield or shieldplate may extend outwards from the front side of the antenna module.

In a possible implementation form of the first aspect, theelectromagnetic absorber shield or electromagnetic absorbing materialcomprises a carbon loaded foam material, such as a carbon loaded foamtape.

In a possible implementation form of the first aspect, theelectromagnetic absorber shield or electromagnetic absorbing materialhas a thickness in the range of 4-12 mm, such as in the range of 5-10mm, such as in the range of 5-8 mm, such as about 6 mm.

In a possible implementation form of the first aspect, then for one orboth antenna modules, the first antenna array holds a number of parallelplate blinds secured to the front side of the first antenna arraybesides or between the cavity slots and substantially perpendicular tothe longitudinal direction of the waveguide columns of the first antennaarray.

In a possible implementation form of the first aspect, then for one orboth antenna modules, the second antenna array holds a number ofparallel plate blinds secured to the front side of the second antennaarray besides or between the cavity slots and substantiallyperpendicular to the longitudinal direction of the waveguide columns ofthe second antenna array.

The plate blinds are vertical blinds or baffles for reducingelectromagnetic power radiated in the cross-polarization, that is blindsor baffles for cross-polarization suppression. The plate blinds may besubstantially U-shaped with two parallel side plates and a bottom plate.

By having the electromagnetic absorbing shield between the radiatingarray and the receiving array, and by having the lower and upperelectromagnetic absorbing shields, the internal reflection ofelectromagnetic signals between and alongside the vertical plate blindsis reduced.

In a possible implementation form of the first aspect, each or at leastpart of the plate blinds is secured to the front side of thecorresponding antenna array by one or more sliding dovetail joints.

The tail of a dovetail joint may be formed at a bottom part of the plateblind and the socket of the dovetail joint may be formed in at least theoutermost positioned waveguide columns of the antenna array. Thewaveguide columns with no dovetail socket may hold a cut-outcorresponding to the width of the bottom of the plate blinds. The use ofdovetail joints and cut-outs serves to increase the mechanicalstabilization of the arrays, and to keep the waveguide columns inalignment.

In a possible implementation form of the first aspect, then for one orboth antenna modules, the waveguide columns of the first and secondantenna arrays are of equal length.

In a possible implementation form of the first aspect, then for one orboth antenna modules, the first ends of the waveguide columns of boththe first and second antenna arrays are aligned in a directionperpendicular to the longitudinal direction of the waveguide columns,and the second ends of the waveguide columns of both the first andsecond antenna arrays are also aligned in a direction perpendicular tothe longitudinal direction of the waveguide columns.

In a possible implementation form of the first aspect, then for one orboth antenna modules, the waveguide columns of both the first and secondantenna arrays hold an absorbing load within the second column end.

By having aligned waveguide columns with absorbing loads, the antennaarrays may function in the travelling wave mode.

In a possible implementation form of the first aspect, then for one orboth antenna modules, the number of waveguide columns in the secondreceiving array is larger than the number of waveguide columns in thefirst radiating array.

In a possible implementation form of the first aspect, then for one orboth antenna modules, the number of waveguide columns in the secondreceiving array is twice the number of waveguide columns in the firstradiating array.

In a possible implementation form of the first aspect, then for one orboth antenna modules, the first radiating array comprises four waveguidecolumns, and the second receiving array comprises eight waveguidecolumns.

In a possible implementation form of the first aspect, then for one orboth antenna modules, a radiating signal probe is operably disposed ineach column of the first antenna array, and a receiving signal probe isoperably disposed in each column of the second antenna array.

In a possible implementation form of the first aspect, then for eachwaveguide column holding a signal probe, the signal probe is disposedproximal to the first end of the waveguide column. The signal probes maybe loop probes with a loop or an open-ended loop for emitting and/orreceiving the electromagnetic signal.

In a possible implementation form of the first aspect, the systemfurther comprises a signal generating system holding a single signalgenerator, and the first antenna module holds first electronic transmitcircuitry configured for feeding the first radiating array of the firstantenna module to radiate first electromagnetic signals, and the secondantenna module holds second electronic transmit circuitry configured forfeeding the first radiating array of the second antenna module toradiate second electromagnetic signals, said first and secondelectromagnetic signals being fully synchronized electromagnetic signalsbased at least partly on signals provided by said single signalgenerator.

In a possible implementation form of the first aspect, the first antennamodule holds first electronic receive circuitry configured forprocessing signals received by the second receiving array of the firstantenna module, and the second antenna module holds second electronicreceive circuitry configured for processing signals received by thesecond receiving array of the second antenna module, said first andsecond electronic receive circuitry being configured for processing thereceived signals in synchronization with the radiated electromagneticsignals, said synchronization being based on signals provided by thesingle signal generator.

In a possible implementation form of the first aspect, the systemfurther comprises:

first processing circuitry for processing signals received by the firstantenna module, said first processing circuitry being configured toprovide first type radar plots of detected objects presented by saidsignals received by the first antenna module; and

second processing circuitry for processing signals received by thesecond antenna module, said second processing circuitry being configuredto provide second type radar plots of detected objects presented by saidsignals received by the second antenna module.

In a possible implementation form of the first aspect, the systemfurther comprises:

radar track processing circuitry, said radar track processing circuitrybeing configured to provide a radar track for a detected object based onboth the first and the second type radar plots.

According to a second aspect there is provided a radar antenna modulecomprising:

a first planar slotted waveguide antenna array configured for radiatingelectromagnetic waves; and

a second slotted waveguide antenna array configured for receivingelectromagnetic waves;

wherein each planar slotted waveguide antenna array comprises severallongitudinal extending waveguide columns disposed in a parallel andadjacent position with respect to one another, said waveguide columnshaving a front side and a rear side with a plurality of cavity slots onthe front side, and said waveguide columns further having first andsecond column ends; and

wherein the first and second antenna arrays are arranged with thewaveguide columns of the first antenna array disposed in a parallelposition to the waveguide columns of the second antenna array.

In a possible implementation form of the second aspect, the front sideof the columns holding the cavity slots of both the first and secondplanar arrays are positioned substantially in the same plane. By havingthe radiating and receiving arrays in the same plane, a simplifiedmanufacture of the antenna module may be obtained.

In a possible implementation form of the second aspect, the cavity slotson the front side of the columns of the first array are arranged in afirst plane, and the cavity slots on the front side of the columns ofthe second array are arranged in a second plane, and the first andsecond arrays are positioned with an angle between said first plane andsaid second plane. This angle should be a blunt or abuse angle, whichmay be closer to 180° than to 90° . By having the radiating andreceiving arrays in angled planes, a higher scanning coverage may beobtained.

In a possible implementation form of the second aspect, the first planarantenna array is a narrow sided slotted waveguide antenna arrayconfigured for radiating horizontal polarized electromagnetic waves, andthe second planar antenna array is a narrow sided slotted waveguideantenna array configured for receiving horizontal polarizedelectromagnetic waves.

In a possible implementation form of the second aspect, the waveguidecolumns of the first and second antenna arrays are of equal length.

In a possible implementation form of the second aspect, anelectromagnetic shield or shield plate is arranged substantiallyparallel to the waveguide columns and between the first radiatingantenna array and the second receiving antenna array, whichelectromagnetic shield or shield plate may extend outwards from thefront side of the antenna module.

In a possible implementation form of the second aspect, theelectromagnetic shield or shield plate is an electromagnetic absorbingshield or shield plate, or the shield or shield plate is fully or atleast partly covered by an electromagnetic absorbing material.

In a possible implementation form of the second aspect, the first planarslotted waveguide antenna array is positioned as a lower radiatingantenna array, and the second slotted waveguide antenna array ispositioned above the first array as an upper receiving antenna array.

In a possible implementation form of the second aspect, a first or lowerelectromagnetic shield or shield plate, which may be a first or lowerelectromagnetic absorbing shield or shield plate, and which may be fullyor at least partly covered by an electromagnetic absorbing material, isarranged substantially parallel to the waveguide columns and below thelowermost waveguide column of the first lower radiating antenna array.This first or lower electromagnetic shield or shield plate may extendoutwards from the front side of the antenna module.

In a possible implementation form of the second aspect, a second orupper electromagnetic shield or shield plate, which may be a second orupper electromagnetic absorbing shield or shield plate, and which may befully or at least partly covered by an electromagnetic absorbingmaterial, is arranged substantially parallel to the waveguide columnsand above the uppermost waveguide column of the second upper receivingantenna array. This electromagnetic second or upper electromagneticshield or shield plate may extend outwards from the front side of theantenna module.

In a possible implementation form of the second aspect, theelectromagnetic absorber shield or electromagnetic absorbing materialcomprises a carbon loaded foam material, such as a carbon loaded foamtape.

In a possible implementation form of the second aspect, theelectromagnetic absorber shield or electromagnetic absorbing materialhas a thickness in the range of 4-12 mm, such as in the range of 5-10mm, such as in the range of 5-8 mm, such as about 6 mm.

In a possible implementation form of the second aspect, the firstantenna array holds a number of parallel plate blinds secured to thefront side of the first antenna array besides or between the cavityslots and substantially perpendicular to the longitudinal direction ofthe waveguide columns of the first antenna array.

In a possible implementation form of the second aspect, the secondantenna array holds a number of parallel plate blinds secured to thefront side of the second antenna array besides or between the cavityslots and substantially perpendicular to the longitudinal direction ofthe waveguide columns of the second antenna array. The plate blinds arevertical blinds or baffles for reducing electromagnetic power radiatedin the cross-polarization, that is blinds or baffles forcross-polarization suppression. The plate blinds may be substantiallyU-shaped with two parallel side plates and a bottom plate.

By having the electromagnetic absorbing shield between the radiatingarray and the receiving array, and by having the lower and upperelectromagnetic absorbing shields, the internal reflection ofelectromagnetic signals between and alongside the vertical plate blindsis reduced.

In a possible implementation form of the second aspect, each or at leastpart of the plate blinds is secured to the front side of thecorresponding antenna array by one or more sliding dovetail joints. Thetail of a dovetail joint may be formed at a bottom part of the plateblind and the socket of the dovetail joint may be formed in at least theoutermost positioned waveguide columns of the antenna array. Thewaveguide columns with no dovetail socket may hold a cut-outcorresponding to the width of the bottom of the plate blinds. The use ofdovetail joints and cut-outs serves to increase the mechanicalstabilization of the arrays, and to keep the waveguide columns inalignment.

In a possible implementation form of the second aspect, the first endsof the waveguide columns of both the first and second antenna arrays arealigned in a direction perpendicular to the longitudinal direction ofthe waveguide columns, and the second ends of the waveguide columns ofboth the first and second antenna arrays are also aligned in a directionperpendicular to the longitudinal direction of the waveguide columns.

In a possible implementation form of the second aspect, the waveguidecolumns of both the first and second antenna arrays hold an absorbingload within the second column end. By having aligned waveguide columnswith absorbing loads, the antenna arrays may function in the travellingwave mode.

In a possible implementation form of the second aspect, the number ofwaveguide columns in the second receiving array is larger than thenumber of waveguide columns in the first radiating array. In a possibleimplementation form of the second aspect, the number of waveguidecolumns in the second receiving array is twice the number of waveguidecolumns in the first radiating array. In a possible implementation formof the second aspect, the for one or both antenna modules, the firstradiating array comprises four waveguide columns, and the secondreceiving array comprises eight waveguide columns.

In a possible implementation form of the second aspect, a radiatingsignal probe is operably disposed in each column of the first antennaarray, and a receiving signal probe is operably disposed in each columnof the second antenna array. In a possible implementation form of thesecond aspect, then for each waveguide column holding a signal probe,the signal probe is disposed proximal to the first end of the waveguidecolumn. The signal probes may be loop probes with a loop or anopen-ended loop for emitting and/or receiving the electromagneticsignal.

A back-to-back radar antenna system may be provided by using two radarantenna modules, where each antenna module is selected from the possibleimplementation forms of the antenna module according to the secondaspect.

It is an object of the aspects of the disclosed embodiments to provide acavity slotted-waveguide antenna array system, which reduces falsereflections from the radiating antenna to the receiving antenna.

According to a third aspect there is provided a radar system comprisinga first radar antenna module comprising:

a first planar slotted waveguide antenna array configured for radiatingelectromagnetic waves, and

a second planar slotted waveguide antenna array configured for receivingelectromagnetic waves, wherein:

each planar slotted waveguide antenna array comprises severallongitudinal extending waveguide columns disposed in a parallel andadjacent position with respect to one another, said waveguide columnshaving a front side and a rear side with a plurality of cavity slots onthe front side, and said waveguide columns further having first andsecond column ends;

the waveguide columns of the first and second antenna arrays have equalinternal height and equal internal width;

the first and second antenna arrays are arranged with the waveguidecolumns of the first antenna array disposed in a parallel position tothe waveguide columns of the second antenna array;

the front side of the columns holding the cavity slots of the firstplanar antenna array are positioned in a first plane and the front sideof the columns holding the cavity slots of the second planar antennaarray are positioned in a second plane parallel to said first plane; and

the first and second antenna arrays are positioned at a distance to eachother with a longitudinal extending outer sidewall of an outermostwaveguide column of the first array arranged closest to a longitudinalextending outer sidewall of an outermost waveguide column of the secondarray, said closest outer sidewalls of the outermost columns of thefirst and second antenna arrays positioned with a minimum parallelcolumn distance to each other in a direction parallel to the first andsecond planes, said minimum parallel column distance being at least 10times the internal width of the waveguide columns.

By having the first radiating antenna array and the second receivingantenna array offset to each other in a direction parallel to the firstand second planes, the amount of false reflections from the radiatingantenna array reaching the receiving antenna array will be reduced,thereby improving the signal to noise ratio.

In a possible implementation form of the third aspect, said minimumparallel column distance is at least 12 times or at least 15 times theinternal width of the waveguide columns.

In a possible implementation form of the third aspect, the first andsecond parallel planes are offset with a minimum perpendicular arraydistance to each other in a direction perpendicular to said planes. In apossible implementation form of the third aspect, said minimumperpendicular array distance is at least 3 times or at least 5 times theinternal width of said waveguide columns.

According to a fourth aspect there is provided a radar system comprisinga first radar antenna module comprising:

a first planar slotted waveguide antenna array configured for radiatingelectromagnetic waves, and

a second planar slotted waveguide antenna array configured for receivingelectromagnetic waves, wherein:

each planar slotted waveguide antenna array comprises severallongitudinal extending waveguide columns disposed in a parallel andadjacent position with respect to one another, said waveguide columnshaving a front side and a rear side with a plurality of cavity slots onthe front side, and said waveguide columns further having first andsecond column ends;

the waveguide columns of the first and second antenna arrays have equalinternal height and equal internal width;

the first and second antenna arrays are arranged with the waveguidecolumns of the first antenna array disposed in a parallel position tothe waveguide columns of the second antenna array;

the front side of the columns holding the cavity slots of the firstplanar antenna array are positioned in a first plane and the front sideof the columns holding the cavity slots of the second planar antennaarray are positioned in a second plane parallel to said first plane; and

the first and second parallel planes are offset with a minimumperpendicular array distance to each other in a direction perpendicularto said planes.

In a possible implementation form of the fourth aspect, said minimumperpendicular array distance is at least 3 times or at least 5 times theinternal width of said waveguide columns.

By having the first radiating antenna array and the second receivingantenna array offset to each other in the direction perpendicular to thefirst and second planes, the resulting antenna module may take up lessspace in the horizontal direction, which is useful when the antennamodule is used in a rotating antenna system. Furthermore, by having thefirst radiating antenna array and the second receiving antenna arrayoffset to each other in the direction perpendicular to the first andsecond planes, the amount of false reflections from the radiatingantenna array reaching the receiving antenna array may be reduced,thereby improving the signal to noise ratio.

In a possible implementation form of the fourth aspect, the firstantenna and second antenna arrays are positioned at a distance to eachother with a longitudinal extending outer sidewall of an outermostwaveguide column of the first array arranged closest to a longitudinalextending outer sidewall of an outermost waveguide column of the secondarray, said closest outer sidewalls of the outermost columns of thefirst and second antenna arrays positioned with a minimum parallelcolumn distance to each other in a direction parallel to the first andsecond planes, said minimum parallel column distance being at least 2times the internal width of the waveguide columns. In a possibleimplementation form of the fourth aspect, said minimum parallel columndistance is at least 3 times, such as at least 5 times, such as at least10 times, such as at 12 times or at least 15 times the internal width ofthe waveguide columns.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the front sides of the firstand second antenna arrays face the same direction being a frontdirection of the antenna module.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first plane is offset fromthe second plane by the perpendicular array distance in a directionopposite to said front direction.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first antenna array has afirst longitudinal extending outermost array sidewall closest to asecond longitudinal extending outermost array sidewall of the secondantenna array, said closest first and second outermost array sidewallspositioned with a minimum parallel array distance to each other in adirection parallel to the first and second planes, said minimum parallelarray distance being smaller than or equal to the minimum parallelcolumn distance.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first outer array sidewallis the outer sidewall of the outermost waveguide column of the firstarray, and the second outer array sidewall is the outer sidewall of theoutermost waveguide column of the second array.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first outer array sidewallis an outer sidewall of a first spacer part connected to said outermostwaveguide column of the first antenna array, and the second outer arraysidewall is an outer sidewall of a second spacer part connected to saidoutermost waveguide column of the second antenna array.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, one or more electromagneticshield(s) is/are arranged between the first radiating antenna array andthe second receiving antenna array.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the front sides of the firstand second antenna arrays face the same direction being a frontdirection of the antenna module, and at least a part of theelectromagnetic shields extends outwards from the front side of theantenna module.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the one or moreelectromagnetic shields comprise a first shield plate and a secondshield plate with both shield plates having a first direction ofextension and a second direction of extension perpendicular to the firstdirection of extension. In a possible implementation form of the thirdaspect or in a possible implementation for of the fourth aspect, thefirst direction of extension for both shield plates is parallel to thelongitudinal extension of the waveguides.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first shield plate has afirst outer edge in contact with said first outermost array sidewall ofthe first array and the second shield plate has a first outer edge incontact with said second outermost array sidewall of the second array.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the second direction ofextension of the first shield plate has a first obtuse angle to thefront side of the first array and the second direction of extension ofthe second shield plate has a second obtuse angle to the front side ofthe second array.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the second direction ofextension of the first shield plate differs from the second direction ofextension of the second shield plate, and the second direction ofextension of the first shield plate forms a first acute angle to thesecond direction of extension of the second shield plate.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first and second shieldplates reach a point or line of contact along said second directions ofextension.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first shield plate has afirst maximum length of extension in its second direction of extensionand the second shield plate has a second maximum length of extension inits second direction extension, said first and second maximum lengths ofextension being defined by a point or line of contact between the firstand second shields plates.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first antenna array has asecond longitudinal extending outer array sidewall opposite to saidfirst outer array sidewall, and a third shield plate is arranged incontact with said second longitudinal extending outer array sidewall ofthe first array, said third shield plate extending outwards from thefront side of the first antenna array.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the third shield plate has afirst and a second direction of extension, and the first direction ofextension of the third shield plate is parallel to the longitudinalextension of the waveguides.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the second direction ofextension of the third shield plate differs from the second direction ofextension of the first shield plate, and the second direction ofextension of the third shield plate has a third obtuse angle to thefront side of the first array.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first, second and/or thirdobtuse angles are in the range of 100° to 140°, such as 120°.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first acute angle is inthe range of 40° to 80°, such as 60°.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first planar antenna arrayis a narrow sided slotted waveguide antenna array configured forradiating horizontal polarized electromagnetic waves, and the secondplanar antenna array is a narrow sided slotted waveguide antenna arrayconfigured for receiving horizontal polarized electromagnetic waves.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the waveguide columns of thefirst and second antenna arrays are of equal length.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first antenna array holdsa number of parallel plate blinds secured to the front side of the firstantenna array besides or between the cavity slots and substantiallyperpendicular to the longitudinal direction of the waveguide columns ofthe first antenna array.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the second antenna array holdsa number of parallel plate blinds secured to the front side of thesecond antenna array besides or between the cavity slots andsubstantially perpendicular to the longitudinal direction of thewaveguide columns of the second antenna array. The plate blinds arevertical blinds or baffles for reducing electromagnetic power radiatedin the cross-polarization, that is blinds or baffles forcross-polarization suppression. The plate blinds may be substantiallyU-shaped with two parallel side plates and a bottom plate.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the number of waveguidecolumns in the second receiving array is larger than the number ofwaveguide columns in the first radiating array. In a possibleimplementation form of the third aspect or in a possible implementationform of the fourth aspect, the number of waveguide columns in the secondreceiving array is twice the number of waveguide columns in the firstradiating array. In a possible implementation form of the third aspector in a possible implementation form of the fourth aspect, the firstradiating array comprises four waveguide columns, and the secondreceiving array comprises eight waveguide columns.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the radar system furthercomprises a rotation system configured for supporting and rotating thefirst antenna module around a vertical axis.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first radar antenna moduleis secured to the rotation system with the first and second planarantenna arrays positioned with the first and second planes holding asecond acute angle to the vertical axis of rotation.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the radar system furthercomprises a second radar antenna module being configured and dimensionedequal to the first radar antenna module, said second radar antennamodule being supported by the rotation system with the first and secondantenna modules arranged in a back-to-back position on opposite sides ofa plane intersecting the axis of rotation, and with the rear side of thewaveguide columns of the antenna arrays of the first antenna modulefacing the rear side of the waveguide columns of the antenna arrays ofthe second antenna module.

By having a rotating radar system with two back-to-back positionedantenna modules, it is possible to decrease the speed of rotation tohalf the speed of a rotating radar system, which comprises only a singleradar module, while still having the same speed of update of radartracks obtained from received signals being reflected from detectedobjects or targets. By lowering the speed of rotation, a higher signalexposure time on target is obtained, resulting in a higher signal tonoise ratio, which again results in more information of any detectedtarget or object.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the second radar antennamodule is secured to the rotation system with its first and secondplanar antenna arrays positioned with the first and second planesholding said second acute angle to the vertical axis of rotation.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the second acute angle is inthe range of 15° to 25°, such as 20°.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first and second antennaarrays of each radar antenna module are positioned with said first andsecond longitudinal extending outermost array sidewalls reaching asingle axis parallel to said vertical axis of rotation.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the radar system furthercomprises a protective housing in the form of a radome covering saidantenna module(s).

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the radome has a cylindricallyshaped wall part surrounding the antenna module(s), said wall part beingslightly inclined towards the antenna module(s) forming a small acuteinclination angle to said axis of rotation, said small acute angle beingno larger than 10°, such as no larger than 5, such as about 3°.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first and second shieldplates of a radar antenna module each have a second outer edge proximatethe cylindrically wall part of the radome, said second outer edges beingcurve shaped to follow the interior of the cylindrically shaped radome.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the third shield plate of aradar antenna module has a second outer edge proximate the cylindricallywall part of the radome, said second outer edge being curve shaped tofollow the interior of the cylindrically shaped radome.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the distance between thesecond outer edge of one said shield plates and the interior of thecylindrically shaped wall part of the radome is no larger than 15 mm,such as no larger than 10 mm, such as no larger than 8 mm.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first and second antennamodules are arranged in a mirrored position relative to said planeintersecting the vertical axis of rotation.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the radome is made of amaterial having a high electromagnetic transparency, such as made of apolyethylene (PE) or polypropylene (PP) based ultra heigh molecularweight plastic material.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the radome is made of amaterial having a thickness in the range of 1-3 mm, such as in the rangeof 1-2 mm or such as in the range of 1-1.5 mm.

When having two back-to-back simultaneously operating antenna modules,it is important to minimize reflection of signals transmitted orradiated from the radiating array of one module to the receiving arrayof the other module. By reducing the material thickness of the radome,the electromagnetic transparency of the radome is increased, therebyminimizing the internal reflection from the radome. By using a PE or PPbased material, such as a PE or PP based ultra heigh molecular weightplastic material, the electromagnetic transparency of the radome isincreased even further.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the system further comprises asignal generating system holding a single signal generator, and thefirst antenna module holds first electronic transmit circuitryconfigured for feeding the first radiating array of the first antennamodule to radiate first electromagnetic signals, and the second antennamodule holds second electronic transmit circuitry configured for feedingthe first radiating array of the second antenna module to radiate secondelectromagnetic signals, said first and second electromagnetic signalsbeing fully synchronized electromagnetic signals based at least partlyon signals provided by said single signal generator.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the first antenna module holdsfirst electronic receive circuitry configured for processing signalsreceived by the second receiving array of the first antenna module, andthe second antenna module holds second electronic receive circuitryconfigured for processing signals received by the second receiving arrayof the second antenna module, said first and second electronic receivecircuitry being configured for processing the received signals insynchronization with the radiated electromagnetic signals, saidsynchronization being based on signals provided by the single signalgenerator.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the system further comprises:

first processing circuitry for processing signals received by the firstantenna module, said first processing circuitry being configured toprovide first type radar plots of detected objects presented by saidsignals received by the first antenna module; and

second processing circuitry for processing signals received by thesecond antenna module, said second processing circuitry being configuredto provide second type radar plots of detected objects presented by saidsignals received by the second antenna module.

In a possible implementation form of the third aspect or in a possibleimplementation form of the fourth aspect, the system further comprises:

radar track processing circuitry, said radar track processing circuitrybeing configured to provide a radar track for a detected object based onboth the first and the second type radar plots.

The foregoing and other objects are achieved by the features of theindependent claims. Further implementation forms are apparent from thedependent claims, the description and the figures. These and otheraspects of the disclosed embodiments will be apparent from theembodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present disclosure, thedisclosed embodiments will be explained in more detail with reference tothe example embodiments shown in the drawings, in which:

FIG. 1a is a schematic block diagram illustrating the basic structure ofa scanning radar system according to a first example embodiment;

FIGS. 1b and 1c are schematic cross-sectional views illustrating aback-to-back to arrangement of antenna modules for the radar system ofFIG. 1a according to an example embodiment;

FIG. 2a is a schematic block diagram illustrating the basic structure ofa detection system holding a radar system according to a second exampleembodiment;

FIGS. 2b and 2c are schematic cross-sectional views illustrating aback-to-back to arrangement of antenna modules for the radar system ofFIG. 2a according to an example embodiment;

FIGS. 3 a, b, c illustrates manufacturing of an array of slotted cavitycolumns for use in a planar cavity slotted-waveguide antenna arrayaccording to an example embodiment, with FIG. 3a illustratingmanufacturing of a first one-piece metal element, and FIGS. 3b and 3cillustrating manufacturing of a second one-piece metal;

FIG. 4 is a bottom view illustrating further manufacturing steps of acavity slotted-waveguide antenna array according to an exampleembodiment;

FIG. 5 shows a cavity slotted-waveguide antenna array holding plateblinds according to an example embodiment;

FIGS. 6a and 6b show a cut through end view and an enlarged cut out viewof a cavity slotted-waveguide antenna array with signal probes insertedaccording to an example embodiment;

FIGS. 7a and 7b are perspective and side views, respectively, of acavity slotted waveguide antenna array holding both a radiating arrayand a receiving array with absorber shields according to an exampleembodiment;

FIG. 8 is a side view illustrating a back-to-back arrangement of twoantenna modules each holding an antenna array as illustrated in in FIGS.7a and 7b , according to an example embodiment;

FIG. 9 is a side view of a radar antenna module holding a radiatingarray and a receiving array with electromagnetic shields according to anexample embodiment;

FIG. 10 is a schematic cut through view of a radar system holding asingle antenna module as illustrated in FIG. 9 covered by a protectiveradome according to an example embodiment;

FIG. 11 is a schematic cut through view of a radar system holding two ofthe antenna modules illustrated in FIG. 9 with both antenna modulescovered by a protective radome according to an example embodiment;

FIG. 12 is a perspective view illustrating a radar system with aback-to-back arrangement of two antenna modules of the type illustratedin FIG. 9 according to an example embodiment;

FIG. 13 shows the radar antenna module of FIG. 9 with indications ofgeometrical dimensions according to an example embodiment;

FIGS. 14a-14c illustrate scanning of a fixed object using a radar systemholding two back-to-back antenna modules according to an exampleembodiment;

FIGS. 15a-15i illustrate scanning of four moving object using a radarsystem holding two back-to-back antenna modules according to an exampleembodiment;

FIG. 16 is a table giving an overview of the scanning illustrated inFIGS. 15a -15 i; and

FIG. 17 illustrates simultaneous radar image capture for two opposedradar image lines using a radar system holding two back-to-back antennamodules according to an example embodiment.

DETAILED DESCRIPTION

FIG. 1 a is a schematic block diagram illustrating the basic structureof a scanning radar system according to a first example embodiment. Thesystem comprises a rotating scanning radar system 101, which isconfigured to operate as a Frequency Modulated Continuous Wave, FMCW,radar system. The scanning radar system 101 is electronically connectedto a computer system 102. Generated output data may be communicated toan external command and control system 103, where the data may becommunicated by live data streaming, where for example Extensible MarkupLanguage, XML, may be used for streaming.

The scanning radar system 101 holds two back-to-back positioned antennamodules, a first antenna module 110 a and a second antenna module 110 b,where each antenna module 110 a, 110 b comprises a first planar slottedwaveguide antenna array 111 a, 111 b configured for radiatingelectromagnetic waves 113 a, 113 b, and a second planar slottedwaveguide antenna array 112 a, 112 b configured for receivingelectromagnetic waves 114 b. The antennas modules 110 a, 110 b aremounted to a rotation system 116 configured for rotating 117 the antennamodules 110 a, 110 b around a vertical axis 115 at a rotational speed.By having the two simultaneously operating antenna modules 110 a, 110 b,which are both operating as a FMCW radar antenna module, a full 360degree radar image can be obtained for every half rotation of the radarsystem 101. The rotational speed may be of 30 rounds per minute, rpm,whereby a full 360 degree radar image can be obtained every second.

The targets or objects being exposed to the radar signals may includeone or more Unmanned Aerial Vehicles, UAVs, 105 and one or more birds106.

The antenna modules 110 a, 110 b are enclosed by a protecting radome 118having a high electromagnetic transparency in order to minimizereflection of signals transmitted or radiated from the radiating arrays111 a, 111 b to the receiving arrays 112 b, 112 a. In order to obtain ahigh electromagnetic transparency, the radome should be relatively thinand may be made of a material having a thickness in the range of 1-3 mm,such as in the range of 1-2 mm or such as in the range of 1-1.5 mm. Alsoin order to obtain a high electromagnetic transparency, the radome maybe made of a polyethylene (PE) or polypropylene (PP) based ultra heighmolecular weight plastic material. When using a relatively thin wallthickness of below 3 mm, such a in the range of 1-1.5 mm, it ispreferred that the radome 118 has a dome shaped upper part in order toincrease the mechanical strength of the radome 118. The radome 118 isarranged in a fixed position without following the rotation of therotation system 116 and the antenna modules 110 a, 110 b. However, it isalso within an embodiment that the radome 118 is connected to therotation system 116 for being rotated together with the antenna modules110 a, 110 b.

FIGS. 1b and 1c are schematic cross-sectional views illustrating aback-to-back arrangement of the two antenna modules 110 a, 110 b for theradar system 101 of FIG. 1a according to an example embodiment.

For each of the modules 110 a, 110 b of FIGS. 1b and 1 c, anelectromagnetic shield or shield plate 120 a, 120 b is positionedbetween the radiating array 111 a, 111 b and the receiving array 112 a,112 b. A lower electromagnetic shield or shield plate 121 a, 121 b maybe positioned at the lower edge of the radiating array 111 a, 111 b, andan upper electromagnetic shield or shield plate 122 a, 122 b may also bepositioned at an upper edge of the receiving array 112 a, 112 b.

The radar system 101 holds on-board circuitry, which includes a signalgenerating system 125 holding a single signal generator. For theillustrated embodiment of FIGS. 1b and 1 c, the signal generating system125 is positioned at the back of the second antenna module 110 b.

Each of the FMCW radar antenna modules 110 a, 110 b holds electronicon-board circuitry, which includes first electronic transmit circuitry123 a configured for feeding the first radiating array 111 a of thefirst antenna module 110 a to radiate first FMCW electromagnetic signals113 a and positioned at the back of the first antenna module 110 a, andwhich includes second electronic transmit circuitry 123 b configured forfeeding the first radiating array 111 b of the second antenna module 110b to radiate second FMCW electromagnetic signals 113 b and positioned atthe back of the second antenna module 110 b. The first and secondtransmit circuitries 123 a, 123 b are both being fed with signals fromthe signal generating system 125 in order to control the first andsecond electromagnetic signals 113 a, 113 b to be fully synchronizedelectromagnetic signals based at least partly on signals provided by thesingle signal generator of the signal generating system 125.

As part of the electronic on-board circuitry, the first antenna module110 a holds first electronic receive circuitry 124 a configured forprocessing signals received by the second receiving array 112 a of thefirst antenna module 110 a, and the second antenna module 110 b holdssecond electronic receive circuitry 124 b configured for processingsignals received by the second receiving array 112 b of the secondantenna module 110 b. The first electronic receive circuitry 124 a ispositioned at the back of the first antenna module 110 a, and the secondelectronic receive circuitry 124 b is positioned at the back of thesecond antenna module 110 b. The first and second electronic receivecircuitry 124 a, 124 b are configured for processing the receivedsignals in synchronization with the radiated electromagnetic signals 113a, 113 b, which synchronization is based on signals provided by thesingle signal generator of the signal generating system 125.

The on-board circuitry of the radar system 101 also includes a motorcontroller 119 for controlling the rotation system 116. An azimuthencoder may be provided at the rotation system 116, which encoder isconfigured for encoding and communicating the degree of rotation, andthereby the azimuth angle of the antenna modules 110 a, 110 b, at a veryhigh precision. The on-board circuitry also includes signal processingcircuitry 126 for performing first on-board processing of signalsreceived from the first receive circuitry 124 a, and for performingsecond on-board processing of signals received from the second receivecircuitry 124 b, to thereby obtain first digital scan data representingthe electromagnetic signals received by the first antenna module 110 a,and to obtain second digital scan data representing the electromagneticsignals 114 b received by the second antenna module 110 b. The signalprocessing circuitry 126 also provides a control signal to the signalgenerator system 125.

For the illustrated embodiment of FIGS. 1b and 1 c, the signalprocessing circuitry 126 is positioned at the back of the first antennamodule 110 a.

The different circuitries of the on-board circuitry, the signalgenerator system 125, the first and second transmit circuitry 123 a, 123b, the first and second receive circuitry 124 a, 124 b and the signalprocessing circuitry 126 may be enclosed by an aluminium shield, whichshields for electronic noise signals. The on-board signal processingcircuitry 126 may be electronically connected to back end circuitrybeing part of the azimuth encoder for communicating the azimuth angle.The on-board signal processing circuitry 126 and the back end circuitryare electronically connected to the computer system 102, for forwardingthe first and second digital scan data together with data for theazimuth angle to the computer system 102. The electronic signals aretransferred via a glass fibre cable from the signal processing circuitry126 to a rotary joint at the rotation system 116, which is furtherconnected to the computer system 102 by cables.

The computer system 102 may hold first processing circuitry forprocessing the received first digital scan data and azimuth data toprovide first type radar plots of detected objects presented by thesignals received by the first antenna module, and further hold secondprocessing circuitry for processing the received second digital scandata and azimuth data to provide second type radar plots of detectedobjects presented by the signals received by the second antenna module.The computer system 102 may also hold radar track processing circuitryconfigured to provide a radar track for a detected object based on bothfirst and second type radar plots. The computer system 102 may also holdclassifying circuitry for classifying the objects of the tracks.

The scanning radar system 101 of FIG. 1a is based on two antenna modules110 a, 110 b, where each antenna module comprises a first planar slottedwaveguide antenna array 111 a, 111 b configured for radiatingelectromagnetic waves 113 a, 113 b, and a second planar slottedwaveguide antenna array 112 a, 112 b configured for receivingelectromagnetic waves 114 b.

FIG. 2a is a schematic block diagram illustrating the basic structure ofa detection system holding a radar system according to a second exampleembodiment. The detection system comprises a rotating scanning radarsystem 2101, which is configured to operate as a Frequency ModulatedContinuous Wave, FMCW, radar system. The scanning radar system 2101 iselectronically connected to a computer system 2102. Generated outputdata may be communicated to an external command and control system 2103,where the data may be communicated by live data streaming, where forexample Extensible Markup Language, XML, may be used for streaming.

The scanning radar system 2101 holds two back-to-back positioned antennamodules, a first antenna module 2110 a and a second antenna module 2110b, where each antenna module 2110 a, 2110 b comprises a first planarslotted waveguide antenna array 2111 a, 2111 b configured for radiatingelectromagnetic waves 2113 a, 2113 b, and a second planar slottedwaveguide antenna array 2112 a, 2112 b configured for receivingelectromagnetic waves 2114 b. The antennas modules 2110 a, 2110 b aremounted to a rotation system 2116 configured for rotating 2117 theantenna modules 2110 a, 2110 b around a vertical axis 2115 at arotational speed. By having the two simultaneously operating antennamodules 2110 a, 2110 b, which are both operating as a FMCW radar antennamodule, a full 360 degree radar image can be obtained for every halfrotation of the radar system 2101. The rotational speed may be of 30rounds per minute, rpm, whereby a full 360 degree radar image can beobtained every second.

The targets or objects being exposed to the radar signals may includeone or more Unmanned Aerial Vehicles, UAVs, 2105 and one or more birds2106.

The antenna modules 2110 a, 2110 b are enclosed by a protecting radome2118 having a high electromagnetic transparency in order to minimizereflection of signals transmitted or radiated from the radiating arrays2111 a, 2111 b to the receiving arrays 2112 b, 2112 a. In order toobtain a high electromagnetic transparency, the radome should berelatively thin and may be made of a material having a thickness in therange of 1-3 mm, such as in the range of 1-2 mm or such as in the rangeof 1-1.5 mm. Also in order to obtain a high electromagnetictransparency, the radome may be made of a polyethylene (PE) orpolypropylene (PP) based ultra heigh molecular weight plastic material.When using a relatively thin wall thickness of below 3 mm, such a in therange of 1-1.5 mm, it is preferred that the radome 2118 has a domeshaped upper part in order to increase the mechanical strength of theradome 2118. The radome 2118 may be arranged in a fixed position withoutfollowing the rotation of the rotation system 2116 and the antennamodules 2110 a, 2110 b. However, it is also within an embodiment thatthe radome 2118 is connected to the rotation system 2116 for beingrotated together with the antenna modules 2110 a, 2110 b.

FIGS. 2b and 2c are schematic cross-sectional views illustrating aback-to-back arrangement of the two antenna modules 2110 a, 2110 b forthe radar system 2101 of FIG. 2c according to an example embodiment.

For each of the antenna modules 2110 a, 2110 b, the radiating arrays2111 a, 2111 b are positioned at a distance to the receiving arrays 2112b, 2112 a. The radiating arrays 2111 a, 2111 b have a front sidepositioned in a first plane, and the receiving arrays 2112 b, 2112 ahave a front side positioned in a second plane, which second plane maybe parallel to the first plane. When the first and second planes areparallel to each other, the resulting distance between a radiating array2111 a, 2111 b and a corresponding receiving array 2112 a, 2112 b may becomposed of a component in a direction parallel to the first and secondplanes, and a component in a direction perpendicular to the first andsecond planes.

For each of the modules 2110 a, 2110 b of FIGS. 2b and 2c , a firstelectromagnetic shield plate 2120 a, 2120 b and a second electromagneticshield plate 2121 a, 2121 b are positioned between the radiating array2111 a, 2111 b and the receiving array 2112 a, 2112 b. A thirdelectromagnetic shield plate 2122 a, 2122 b may also be positioned at alower edge of the radiating array 2111 a, 2111 b, opposite the firstelectromagnetic shield plate 2121 a, 2121 b.

The radar system 2101 may hold on-board circuitry, which may include asignal generating system 2125 holding a single signal generator. For theillustrated embodiment of FIGS. 2b and 2c , the signal generating system2125 is positioned at the back of the second antenna module 2110 b.

Each of the FMCW radar antenna modules 2110 a, 2110 b may holdelectronic on-board circuitry, which includes first electronic transmitcircuitry 2123 a configured for feeding the first radiating array 2111 aof the first antenna module 2110 a to radiate first FMCW electromagneticsignals 2113 a and positioned at the back of the first antenna module2110 a, and which may include second electronic transmit circuitry 2123b configured for feeding the first radiating array 2111 b of the secondantenna module 2110 b to radiate second FMCW electromagnetic signals2113 b and positioned at the back of the second antenna module 2110 b.The first and second transmit circuitries 2123 a, 2123 b may both be fedwith signals from the signal generating system 2125 in order to controlthe first and second electromagnetic signals 2113 a, 2113 b to be fullysynchronized electromagnetic signals based at least partly on signalsprovided by the single signal generator of the signal generating system2125.

As part of the electronic on-board circuitry, the first antenna module2110 a may hold first electronic receive circuitry 2124 a configured forprocessing signals received by the second receiving array 2112 a of thefirst antenna module 2110 a, and the second antenna module 2110 b mayhold second electronic receive circuitry 2124 b configured forprocessing signals received by the second receiving array 2112 b of thesecond antenna module 2110 b. The first electronic receive circuitry2124 a may be positioned at the back of the first antenna module 2110 a,and the second electronic receive circuitry 2124 b may be positioned atthe back of the second antenna module 2110 b. The first and secondelectronic receive circuitry 2124 a, 2124 b may be configured forprocessing the received signals in synchronization with the radiatedelectromagnetic signals 2113 a, 2113 b, which synchronization may bebased on signals provided by the single signal generator of the signalgenerating system 2125.

The on-board circuitry of the radar system 2101 may also include a motorcontroller 2119 for controlling the rotation system 2116. An azimuthencoder may be provided at the rotation system 2116, which encoder maybe configured for encoding and communicating the degree of rotation, andthereby the azimuth angle of the antenna modules 2110 a, 2110 b, at avery high precision. The on-board circuitry may also include signalprocessing circuitry 2126 for performing first on-board processing ofsignals received from the first receive circuitry 2124 a, and forperforming second on-board processing of signals received from thesecond receive circuitry 2124 b, to thereby obtain first digital scandata representing the electromagnetic signals received by the firstantenna module 2110 a, and to obtain second digital scan datarepresenting the electromagnetic signals 2114 b received by the secondantenna module 2110 b. The signal processing circuitry 2126 may alsoprovide a control signal to the signal generator system 2125.

For the illustrated embodiment of FIGS. 2b and 2c , the signalprocessing circuitry 2126 is positioned at the back of the first antennamodule 2110 a.

The different circuitries of the on-board circuitry, the signalgenerator system 2125, the first and second transmit circuitry 2123 a,2123 b, the first and second receive circuitry 2124 a, 2124 b and thesignal processing circuitry 2126 may be enclosed by an aluminium shield,which shields for electronic noise signals. The on-board signalprocessing circuitry 2126 may be electronically connected to back-endcircuitry being part of the azimuth encoder for communicating theazimuth angle. The on-board signal processing circuitry 2126 and theback-end circuitry may be electronically connected to the computersystem 2102, for forwarding the first and second digital scan datatogether with data for the azimuth angle to the computer system 2102.The electronic signals may be transferred via a glass fibre cable fromthe signal processing circuitry 2126 to a rotary joint at the rotationsystem 2116, which is further connected to the computer system 2102 bycables.

The computer system 2102 may hold first processing circuitry forprocessing the received first digital scan data and azimuth data toprovide first type radar plots of detected objects presented by thesignals received by the first antenna module, and further hold secondprocessing circuitry for processing the received second digital scandata and azimuth data to provide second type radar plots of detectedobjects presented by the signals received by the second antenna module.The computer system 2102 may also hold radar track processing circuitryconfigured to provide a radar track for a detected object based on bothfirst and second type radar plots. The computer system 2102 may alsohold classifying circuitry for classifying the objects of the tracks.

The scanning radar system 2101 of FIG. 2a is based on two antennamodules 2110 a, 2110 b, where each antenna module comprises a firstplanar slotted waveguide antenna array 2111 a, 2111 b configured forradiating electromagnetic waves 2113 a, 2113 b, and a second planarslotted waveguide antenna array 2112 a, 2112 b configured for receivingelectromagnetic waves 2114 b.

FIGS. 3 a, b, c illustrates manufacturing of an array of slotted cavitycolumns for use in a planar cavity slotted-waveguide antenna arrayaccording to an example embodiment, with FIG. 3a illustratingmanufacturing of a first one-piece metal element, and FIGS. 3b and 3cillustrating manufacturing of a second one-piece metal.

FIG. 4 is a bottom view illustrating further manufacturing steps of acavity slotted-waveguide antenna array according to an exampleembodiment.

FIG. 3a illustrates manufacturing of a first one-piece metal element201, which is a first single flat piece of metal, where a plurality oflongitudinally extending parallel and equidistantly arranged open rearcolumn portions 203 a of equal dimensions are formed in the first flatpiece of metal 201. In order to save weight of the final array, grooves204 may be formed in the metal material left between the rear columnportions 203 a.

FIGS. 3b and 3c illustrate manufacturing of a second one-piece metalelement 202, which is a second single flat piece of metal, where aplurality of longitudinally extending parallel and equidistantlyarranged open front column portions 203 b of equal dimensions are formedin the second flat piece of metal 202. The front column portions 203 bhave a width and a length equal to the width and length of the rearcolumn portions 203 a, and the front column portions 203 b are arrangedwith a spacing equal to the spacing of the rear column portions 203 a.After formation of the front column portions 203 b, a plurality oflongitudinally extending parallel front recesses 205 are formed in thesecond metal element 202. These front recesses 205 extend into thesecond metal element 202 from the front surface of the element 202, andthe front recesses 205 define first and second sidewalls 206, 207 of afront part of the front column portions 203 b. After the formation ofthe front recesses 205, a plurality of slots 208 are formed in the frontcolumn portions 203 b. Each slot 208 extends from the bottom of thecorresponding front column portion 203 b to a front surface 209 of thesecond metal element 202.

A signal probe hole 210 is formed at the bottom of the rear columnportions 203 a, where each probe hole extends from the bottom of thecorresponding rear column portion 203 a to a rear surface 211 of thefirst metal element 201. When the slots 208 and probe holes 210 havebeen formed, the first and the second metal elements 201 and 202 areconnected together with the openings of the rear column portions 203 afacing the openings of the front column portions 203 b. The connectionof the first and second metal elements 201 and 202 forms a housing,which comprises a number of parallel slotted-waveguide columns 203having a rectangular cross-section, see FIG. 5, where the parallelslotted-waveguide columns 203 are formed by the rear and front columnportions 203 a, 203 b. The arrangement of the probe holes 210 at therear surface 211 of the first metal element 201 is illustrated in FIG.4, which also shows the first and second metal elements 201 and 202being connected together. The diameter of the probe hole 210 may equalthe internal width of the columns 203 or rear column portions 203 a. InFIG. 4 is also shown screw holes 220, which are provided at the rearsurface 211 of the first metal element 201 in between the rear columnportions 203 a. The screw holes 220 may hold screws connecting the firstand second metal elements 201 and 202.

The material used for the metal elements 201 and 202 may be anodizedaluminum. Is it preferred that the formation of the rear column portions203 a and grooves 204 in the first metal element 201, the formation ofthe front column portions 203 b, the front recesses 205, and the slots208 in the second metal element 202 are performed by use of milling. Theprobe holes 210 may also be formed in the first metal element 201 bydrilling.

FIG. 5 shows part of a cavity slotted-waveguide antenna array 200, whichhas been manufactured and assembled as described above in connectionwith FIGS. 3 a,b,c and FIG. 4. According to an example embodiment, thearray 200 is further provided with a number of conductive parallel plateblinds 212, which are conductively secured to the front side or surface209 of the housing holding the waveguide columns 203 b, 203, where thefront side or surface 209 holds the cavity slots 208. The plate blinds212 are arranged substantially perpendicular to the longitudinaldirection of the waveguide columns 203. The plate blinds 212 have twoparallel outer surfaces being first and second parallel outer surfaces,and the blinds 212 are substantially U-shaped with two parallel sideplates and a bottom plate. The plate blinds 212 are secured to the frontside or surface 209 of the housing holding the waveguide columns 203 b,203 by a sliding dovetail joint 213. The tail of a dovetail joint isformed at a bottom part of a U-shaped plate blind 212 and the socket ofthe dovetail joint is formed in the front side or surface 209 of thehousing holding the outermost positioned waveguide columns 203 b, 203.The waveguide columns 203 with no dovetail socket in the front surface209 may hold a cut-out corresponding to the width of the bottom of theplate blinds. The use of dovetail joints and cut-outs serves to increasethe mechanical stabilization of the arrays, and to keep the waveguidecolumns in alignment. The use of plate blinds 212 is optional.

In order for the slotted-waveguide columns 203 to emit or receive anelectromagnetic signal, a signal probe may be inserted in the probe hole210. This is illustrated in FIGS. 6a and 6b , which show a cut throughend view and an enlarged cut out view of a cavity slotted-waveguideantenna array 200 with signal probes 214 inserted in each waveguidecolumn 203, according to an example embodiment.

The array 200 has eight waveguide columns 203 disposed in apredetermined adjacent position with respect to one another, where eachcolumn may be formed by a rear column portion 203 a formed in a firstone-piece metal element 201 and by a front column portion 203 b formedin a second one-piece metal element 202. Each column 203 has a number ofslots 208 formed in the front column portion 203 b, see FIG. 3c , andeach column 203 has an upper and a lower end. The waveguide columns 203have a rectangular cross-section, and the waveguide columns 203 aredefined by two wide inner surfaces being first and second wide innersurfaces, a narrow inner back surface, and narrow inner front surface.The narrow inner front surface and the front side 209 of the housingdefine a narrow front wall holding the cavity slots 208. The slots 208are narrow walled slots or transverse narrow walled slots 208, whichreach from the first inner wide surface to the second wide innersurface.

A signal probe 214 is operably disposed in each column 203 for emittingand/or receiving an electromagnetic signal. The electromagnetic signalmay have a free-space wavelength of λ₀, and the signal propagates withinthe column 203 holding the signal probe 214 as electromagnetic waveswith a corresponding guided signal wavelength λ_(g). For the embodimentillustrated in FIG. 6, the signal probes 214 are open ended loop probeswith an open ended loop disposed at the narrow inner back surfaceopposite and facing the narrow inner front surface of the waveguidecolumn 203 holding the loop probe 214.

The open ended loop of the loop probe 214 is arranged in a directionperpendicular to the longitudinal direction of the waveguide column 203,and the open ended loop probe 214 may be disposed proximal to the lowerend of the column 203 holding the probe 214. According to an embodiment,each column 203 has an absorbing load at its upper end while the lowerend of the waveguide column may be terminated with a short circuitingend geometry (blind end) or an absorbing load, to enable the column 203to function in a travelling wave mode.

The signal probes 214 are formed of an electrically conductive material,such as copper or silver-plated copper, and are electricallynon-conductively secured to the columns 203. The open ended loop of aloop probe 214 forms part of a loop circle, which may have acircumference in the range of ⅓ to ⅔, such as about ½ of the guidedsignal wavelength λ_(g).

The housing holding the waveguide columns 203 has a rear side surface,and a waveguide bottom wall is defined by the narrow inner back surfaceof a waveguide column 203 and the rear side surface of the housing,whereby an outer back surface of the waveguide bottom wall is defined bythe rear side of the housing. The open ended loop probes 214 have aprobe connection part 215 opposite the open ended loop, where the probeconnection part 215 extends through probe holes 210 provided at thewaveguide bottom wall. An enclosure part 218 is disposed between aprinted circuit board, PCB, 217 and the outer back surface of thewaveguide bottom wall, and the loop probe connection part 215 extendsthrough a surrounding part 219 formed by the enclosure part 218 to reachthe printed circuit board 217. An end part of the connection part 215 ofeach of the loop probes 214, which may reach through the PCB 217 by aso-called via, is electrically connected to a corresponding electricalconductive signal trace provided at the front surface of the printedcircuit board 217. The surrounding parts 219 of the enclosure part 218may be formed to fit or fill out the probe holes 210, and the probeholes 210 may have a diameter equal to the internal width of the column203. An electrically non-conductive material 216 surrounds the probeconnection part 215 extending through the enclosure part 218. Theelectrical non-conductive material may comprise or is made of PolyetherEther Ketone, PEEK, plastic. The enclosure part 218 holds sidewalls 222,and a lid 223 is secured to the sidewalls to close off the enclosurepart 218.

The enclosure part 218 is made of an electrical conductive material,such as aluminium. Before securing the enclosure part 218 to the rearside of the array housing holding the waveguide columns, the probes 214and the PCB 217 may be connected to the enclosure part 218. First, eachloop probe 214 is connected to the enclosure part 218 by having theconnection part 215 surrounded by the non-conductive material 216 andarranged within the surrounding part 219 of the enclosure part 218. Theprinted circuit board, PCB, 217 can then be secured to the enclosurepart 218 by screws 221 with the end part of the probe connection part215 reaching through the PCB 217 by the so-called via. The end part ofthe probe connection part 215 can now be soldered or electricalconnected to a corresponding electrical conductive signal trace providedat the front surface of the printed circuit board 217. The PCB 217 has abottom surface facing the enclosure part 218, where the PCB bottomsurface holds electrical conductive ground traces or parts to provide anelectrical ground connection to the enclosure part 218. In anembodiment, the enclosure part 218 is silver plated for maintaining anelectrical connection between the enclosure part 218 and the PCB bottomground traces.

Each PCB signal trace corresponding to a loop probe 214 may have a firsttrace end soldered to the end part 215 of the loop probe 214, and eachof these PCB signal traces is a copper trace, which preferably is formedto obtain a characteristic impedance of 50 Ohm. The PCB signal traceshaving one end electrically corresponding to a loop probe 214, may inthe other end be electrically connected to radio frequency transmitcircuitry, when the array is a transmitting array, or connected toreceive circuitry, when the array is a receiving array, where thetransmit or receive circuitry may be arranged at the front surface ofthe PCB 217. The radio frequency transmit circuitry may comprise a radiofrequency amplifier, and the receive circuitry may comprise apseudomorphic high electron mobility transistor, PHEMT.

FIGS. 7a and 7b are perspective and side views, respectively, showing acavity slotted waveguide antenna array 300 holding both a firstradiating array 300 a and a second receiving array 300 b according to anexample embodiment. The radiating array 300 a and the receiving array300 b may be manufactured and assembled as described above in connectionwith FIGS. 3 to 6. Each of the antenna modules 110 a and 110 b of thesystem 101 of FIG. 1a may hold an antenna array equal to the array 300of FIGS. 7a and 7 b.

For the array 300 of FIGS. 7a and 7b , the waveguide columns within thefirst radiating array 300 a and second receiving array have equaldimensions. The first radiating array 300 a comprises four waveguidecolumns 303 a, and the second receiving array 300 b comprises eightwaveguide columns 303 b. Thus, both antenna modules 110 a and 110 b mayhave equal dimensioned waveguide columns 303 a, 303 b, whereby it ispossible to operate within the same frequency band for both antennamodules.

For the array 300, the front side of the columns 303 a, 303 b holdingthe cavity slots 208, see FIG. 3c , of both the first and second antennaarrays 300 a, 300 b are positioned substantially in the same plane. Byhaving the radiating and receiving arrays in the same plane, asimplified manufacture of the antenna module may be obtained. Thewaveguide columns 303 a, 303 b of the first and second antenna arrays300 a, 300 b are of equal length, and first ends of the waveguidecolumns 303 a, 303 b of both the first and second antenna arrays 300 a,300 b are aligned in a direction perpendicular to the longitudinaldirection of the waveguide columns 303 a, 303 b, and opposite secondends of the waveguide columns 303 a, 303 b of both the first and secondantenna arrays 300 a, 300 b are also aligned in a directionperpendicular to the longitudinal direction of the waveguide columns 303a, 303 b.

The first radiating antenna array 300 a holds a number of parallel plateblinds 312 a secured to the front side of the first antenna array 300 abesides or between the cavity slots and substantially perpendicular tothe longitudinal direction of the waveguide columns 303 a of the firstantenna array, and the second receiving antenna array 300 b holds anumber of parallel plate blinds 312 b secured to the front side of thesecond antenna array 300 b besides or between the cavity slots andsubstantially perpendicular to the longitudinal direction of thewaveguide columns 303 b of the second antenna array. The plate blinds312 a, 312 b are vertical blinds or baffles for reducing electromagneticpower radiated in the cross-polarization, that is blinds or baffles forcross-polarization suppression. The plate blinds 312 a, 312 b may besubstantially U-shaped with two parallel side plates and a bottom plate.

A radiating signal probe, not shown in FIGS. 7a and 7b , see the probe214 of FIGS. 6a and 6 b, is operably disposed proximal to a first end ineach column 303 a of the first antenna array 300 a, and a receivingsignal probe 214 is operably disposed proximal to a first end in eachcolumn 303 b of the second antenna array 300 b. The waveguide columns303 a, 303 b of both the first and second antenna arrays 300 a, 300 bhold an absorbing load within the second column end. By having alignedwaveguide columns of equal length provided with absorbing loads, theantenna arrays may function in the travelling wave mode.

For the array 300, an electromagnetic shield or shield plate 320 isarranged substantially parallel to the waveguide columns 303 a, 303 band between the first lower radiating antenna array 300 a and the secondupper receiving antenna array 300 b, where the shield or shield plate320 extends outwards from the front side of the antenna array 300. Theelectromagnetic shield or shield plate 320 may be an electromagneticabsorbing shield or shield plate, which may be fully or at least partlycovered by an electromagnetic absorbing material. The array 300 alsoholds a lower electromagnetic shield or shield plate 321, which may bean electromagnetic absorbing shield or shield plate, and which may befully or at least partly covered by an electromagnetic absorbingmaterial, and which is arranged substantially parallel to the waveguidecolumns 303 a and below the lowermost waveguide column 303 a of thefirst lower radiating antenna array 300 a. The lower electromagneticshield or shield plate 321 extends outwards from the front side of theantenna array 300. The array 300 further holds an upper electromagneticshield or shield plate 322, which may be an electromagnetic absorbingshield or shield plate, and which may be fully or at least partlycovered by an electromagnetic absorbing material, and which is arrangedsubstantially parallel to the waveguide columns 303 b and above theuppermost waveguide column 303 b of the second upper receiving antennaarray 300 b. The upper electromagnetic shield or shield plate 322extends outwards from the front side of the antenna array 300. Theheight of the upper and lower electromagnetic shields 322 and 321 shouldbe at least equal to the height of the plate blinds 312 a, 321 b. Theheight of the electromagnetic shield or shield plate 320 between thefirst lower radiating antenna array 300 a and the second upper receivingantenna array 300 b should also be at least equal to the height of theplate blinds 312 a, 321 b, and preferably the height of the shield 320is higher than the height of the upper and lower absorbers shields 322and 321.

The electromagnetic absorber shield or electromagnetic absorbingmaterial may comprise a carbon loaded foam material, such as a carbonloaded foam tape. The electromagnetic absorber shield or electromagneticabsorbing material may have a thickness in the range of 4-12 mm, such asin the range of 5-10 mm, such as in the range of 5-8 mm, such as about 6mm.

By having the electromagnetic shield or shield plate 320 between theradiating array 300 a and the receiving array 300 b, and by having thelower and upper electromagnetic shields or shield plates 321 and 322,the internal reflection of electromagnetic signals between and alongsidethe vertical plate blinds 312 a, 312 b is reduced.

In an embodiment, part of the dimensions of the array 300 are asfollows: the total length of the array 300 and the columns 303 a, 303 bis 420 mm; the total width of the array 300 is 282 mm; the length of theplate blinds 312 a covering the four columns 303 a of the radiatingarray 300 a is 73 mm; the length of the plate blinds 312 b covering theeight columns 303 b of the receiving array 300 b is 153 mm; distancebetween closest side walls of neighboring plate blinds 412 is 14.5 mm;height of the electromagnetic shield or shield plate 320 when measuredfrom the top or front side of the array 300 is 50 mm; height of thelower electromagnetic shield or shield plate 321 when measured from thetop or front side of the array 300 a is 20 mm; height of the upperelectromagnetic shield or shield plate 322 when measured from the top orfront side of the array 300 b is 20 mm.

FIG. 8 is a side view illustrating a back-to-back to arrangement 400 oftwo antenna modules 410 a and 410 b each holding an antenna arraysimilar to the array 300 as illustrated in in FIGS. 7a and 7b ,according to an example embodiment. The first antenna module 410 a holdsa first and lower radiating array 400 aa with four waveguide columns 403aa and a second higher receiving array 400 ba with eight waveguidecolumns 403 ba. Both the first and second arrays 400 aa and 400 ba holdsplate blinds 412 aa and 412 ba, respectively, arranged perpendicular tothe longitudinal direction of the waveguide columns 403 aa, 403 ba.

An electromagnetic shield or shield plate 420 a is arrangedsubstantially parallel to the waveguide columns 403 aa, 403 ba andbetween the first lower radiating antenna array 400 aa and the secondupper receiving antenna array 400 ba. A lower electromagnetic shield orshield plate 421 a is arranged substantially parallel to the waveguidecolumns 403 aa and below the lowermost waveguide column 403 aa of thefirst lower radiating antenna array 400aa. An upper electromagneticshield or shield plate 422 a is arranged substantially parallel to thewaveguide columns 403 ba and above the uppermost waveguide column 403 baof the second upper receiving antenna array 400 ba.

Similar to the first antenna module 410 a, the second antenna module 410b holds a first and lower radiating array 400 ab with four waveguidecolumns 403 ab and a second higher receiving array 400 bb with eightwaveguide columns 403 bb. Both the first and second arrays 400 ab and400 bb holds plate blinds 412 ab and 412 bb, respectively, arrangedperpendicular to the longitudinal direction of the waveguide columns 403ab, 403 bb.

An electromagnetic shield or shield plate 420 b is arrangedsubstantially parallel to the waveguide columns 403 ab, 403 bb andbetween the first lower radiating antenna array 400 ab and the secondupper receiving antenna array 400 bb. A lower electromagnetic shield orshield plate 421 b is arranged substantially parallel to the waveguidecolumns 403 ab and below the lowermost waveguide column 403 ab of thefirst lower radiating antenna array 400 ab. An upper electromagneticshield or shield plate 422 b is arranged substantially parallel to thewaveguide columns 403 bb and above the uppermost waveguide column 403 bbof the second upper receiving antenna array 400 bb.

The first antenna module 410 a also holds on-board circuitry includingsignal processing circuitry 426 a and electronic transmit circuitry 423a, not shown in FIG. 8, and electronic receive circuitry 424 a, notshown in FIG. 8. The second antenna module 410 b also holds on-boardcircuitry including signal generating system 425, not shown in FIG. 8,and electronic transmit circuitry 423 b, and electronic receivecircuitry 424 b. The arrangement 400 is supported by a rotation system416 and holds a motor controller 419 for controlling the rotation system416.

For the arrangement 400 of FIG. 8, the first and second antenna modules410 a and 410 b are arranged in a mirrored position relative to a planeintersecting the vertical axis of rotation, see axis 115 of FIG. 1. Thecavity slots on the front side of the columns 403 aa and 403 ba of thefirst and second antenna arrays 400 aa and 400 ba of the first antennamodule 410 a are arranged in a partially upwards facing plane having afirst acute angle to the vertical direction. Also, the cavity slots onthe front side of the columns 403 ab and 403 bb of the first and secondantenna arrays 400 ab and 400 bb of the second antenna module 401 b arearranged in a partially upwards facing plane having a second acute angleto the vertical direction. When the antenna modules 410 a and 410 b arein the mirrored position, the first acute angle is substantial equal tothe second acute angle. It is preferred that the first and second acuteangles are in the range of 10-30°, such as about 20°.

FIG. 9 is a side view of a radar antenna module 510 holding a firstradiating array 500 a and a second receiving array 500 b withelectromagnetic shields 520, 521, 522 according to an exampleembodiment.

The radiating array 500 a and the receiving array 500 b may bemanufactured and assembled as described above in connection with FIGS. 3to 6. Each of the antenna modules 2110 a and 2110 b of the system 2101of FIG. 2a may hold a radiating and a receiving antenna array 500 a, 500b equal to the arrays 500 a and 500 b of the module 510 of FIG. 9.

For the module 510 of FIG. 9, the waveguide columns 503 a and 503 bwithin the first radiating array 500 a and second receiving array 503 bhave equal dimensions. The first radiating array 500 a comprises fourwaveguide columns 503 a, and the second receiving array 500 b compriseseight waveguide columns 503 b. Thus, both antenna modules 2110 a and2110 b may have equal dimensioned waveguide columns 503 a, 503 b,whereby it is possible to operate within the same frequency band forboth antenna modules.

For the module 510, the radiating array 500 a is positioned at adistance to the receiving array 500 b. The radiating array 500 a has afront side positioned in a first plane, and the receiving array 500 bhas a front side positioned in a second plane, which second plane isparallel to the first plane. Thus, the front sides of the firstradiating array 500 a and the second receiving arrays 500 b face thesame direction being a front direction of the antenna module 510. Whenthe first and second planes are parallel to each other, the resultingdistance between the radiating array 500 a and the receiving array 500 bholds a distance component in a direction parallel to the first andsecond planes, and a distance component in a direction perpendicular tothe first and second planes. The first plane is offset from the secondplane by said perpendicular distance component in a direction oppositeto the front direction of the module 510. This perpendicular distancecomponent is in the following referred to as perpendicular arraydistance.

By having the radiating array 500 a and the receiving array 500 b offsetto each other in the direction perpendicular to the first and secondplanes, the resulting module 510 may take up less space in thehorizontal direction when the module 510 is used in a rotating antennasystem such as the system 2101 of FIG. 2a . It is preferred that thefirst and second parallel planes are offset with a minimum perpendiculararray distance, where the minimum perpendicular array distance is atleast 3 times or at least 5 times the internal width of the waveguidecolumns 503 a, 503 b.

The first radiating antenna array 500 a and the second receiving antennaarray 500 b are positioned at a distance to each other with alongitudinal extending outer sidewall of an outermost waveguide columnof the first array 500 a positioned closest to a longitudinal extendingouter sidewall of an outermost waveguide column of the second array 500b. Here, the closest outer sidewalls of these outermost columns of thefirst and second antenna arrays 500 a, 500 b may be positioned with aminimum parallel column distance to each other in a direction parallelto the first and second planes. It is preferred that this minimumparallel column distance is at least 5 times the internal width of thewaveguide columns 503 a, 503 b. It is also within embodiments that thisminimum parallel column distance is at least 10 times, such as at least12 times or at least 15 times the internal width of the waveguidecolumns.

By having the radiating array 500 a and the receiving array 500 b offsetto each other in a direction parallel to the first and second planes,the amount of false reflections from the radiating antenna reaching thereceiving antenna will be reduced, thereby improving the signal to noiseratio.

The module 510 may also hold a support 529 in order to hold the firstand second antenna arrays 500 a and 500 b in the desired position.

The waveguide columns 503 a, 503 b of the first and second antennaarrays 500 a, 500 b are of equal length, and first ends of the waveguidecolumns 503 a, 503 b of both the first and second antenna arrays 500 a,500 b may reach a single plane in a direction perpendicular to thelongitudinal direction of the waveguide columns 503 a, 503 b, andopposite second ends of the waveguide columns 503 a, 503 b of both thefirst and second antenna arrays 500 a, 500 b may reach another singleplane in a direction perpendicular to the longitudinal direction of thewaveguide columns 503 a, 503 b.

The first radiating antenna array 500 a may hold a number of parallelplate blinds 512 a secured to the front side of the first antenna array500 a besides or between the cavity slots and substantiallyperpendicular to the longitudinal direction of the waveguide columns 503a of the first antenna array, and the second receiving antenna array 500b may hold a number of parallel plate blinds 512 b secured to the frontside of the second antenna array 500 b besides or between the cavityslots and substantially perpendicular to the longitudinal direction ofthe waveguide columns 503 b of the second antenna array. The plateblinds 512 a, 512 b are vertical blinds or baffles for reducingelectromagnetic power radiated in the cross-polarization, that is blindsor baffles for cross-polarization suppression. The plate blinds 512 a,512 b may be substantially U-shaped with two parallel side plates and abottom plate.

A radiating signal probe, not shown in FIG. 9, see the probe 214 ofFIGS. 6a and 6b , is operably disposed proximal to a first end in eachcolumn 503 a of the first antenna array 500 a, and a receiving signalprobe 214 is operably disposed proximal to a first end in each column503 b of the second antenna array 500 b. The waveguide columns 503 a,503 b of both the first and second antenna arrays 500 a, 500 b hold anabsorbing load within the second column end. By having aligned waveguidecolumns of equal length provided with absorbing loads, the antennaarrays may function in the travelling wave mode.

For the module 510 of FIG. 9, the first antenna array 500 a has a firstlongitudinal extending outermost array sidewall 526 closest to a secondlongitudinal extending outermost array sidewall 527 of the secondantenna array 500 b, where these closest array sidewalls 526 and 527 arepositioned with a minimum parallel array distance to each other in adirection parallel to the first and second planes. The first antennaarray 500 a has spacer parts 523 and 524 connected to the outermostwaveguide columns 503 a, and the second antenna array 500 b has a spacerpart 525 connected to the outermost waveguide column 503 b closest tothe first antenna array 500 a. The first array sidewall 526 is thesidewall of spacer part 523, the second array sidewall 527 is thesidewall of the lower spacer part 525 of the second antenna array 500 b,while the lower spacer part 524 of the first antenna array has a thirdoutermost array sidewall 528. A spacer part, not shown in FIG. 9, mayalso be provided at the upper side of the second antenna array 500 bopposite the spacer part 525.

For the first and second antenna arrays 500 a, 500 b the spacer parts523, 524 are positioned next to the outermost waveguide columns 503 a,503 b, whereby the minimum parallel array distance is smaller than theminimum parallel column distance. However, it is also within anembodiment that the spacer parts 523 and 525 are omitted, whereby theoutermost array sidewalls 526 and 527 are the outer sidewall of theoutermost waveguide columns of the first antenna array 500 a and theouter sidewall of the closest outermost waveguide of the second antennaarray 500 b, whereby the minimum parallel array distance may be equal tothe minimum parallel column distance.

The first and second antenna arrays 500 a, 500 b may be positioned sothat the upper edges of the outermost array sidewalls 527 and 528 reacha common vertical axis 530 as illustrated in FIG. 9, to thereby reducethe space used in the horizontal direction for the module 510.

For the module 510, a first electromagnetic shield plate 520 and asecond electromagnetic shield plate 521 are positioned between the firstradiating array 500 a and the second receiving array 500 b. Theelectromagnetic shield plates 520, 521 are dimensioned and positioned sothat at least a part of the electromagnetic shield plates 520 and 521extends outwards from the front side of the antenna module 510. Both thefirst shield plate 520 and the second shield plate 521 have a firstdirection of extension and a second direction of extension perpendicularto the first direction of extension, with the first direction ofextension for both shield plates being parallel to the longitudinalextension of the waveguides 503 a, 503 b. The second direction ofextension of the first shield plate 520 forms a first obtuse angle α1,see FIG. 13, to the front side of the first array 500 a, and the seconddirection of extension of the second shield plate 521 forms a secondobtuse angle α2, see FIG. 13, to the front side of the second array 500b. The first and second shield plates 520, 521 reach a point or line ofcontact along their second directions of extension, with seconddirection of extension of the first shield plate 520 forming a firstacute angle α4, see FIG. 13, to the second direction of extension of thesecond shield plate 521.

A third electromagnetic shield plate 522 may also be positioned at alower edge of the first radiating array 500 a, opposite the firstelectromagnetic shield plate 520. The electromagnetic shield plate 522is dimensioned and positioned so that at least a part of theelectromagnetic shield plate 522 extends outwards from the front side ofthe first radiating array 500 a. The third shield plate 522 also has afirst direction of extension and a second direction of extensionperpendicular to the first direction of extension, where the firstdirection of extension of the third shield plate 522 is parallel to thelongitudinal extension of the waveguides 503 a, and where the seconddirection of extension of the third shield plate 522 forms a thirdobtuse angle α3, see FIG. 13, to the front side of the first array 500a. The use of the third electromagnetic shield plate 522 is optional. Afourth electromagnetic shield plate, not shown in FIG. 9, may also bepositioned at an upper edge of the first receiving array 500 b, oppositethe second electromagnetic shield plate 521. The fourth shield plate mayalso have a first direction of extension of the third shield plateparallel to the longitudinal extension of the waveguides 503 b, and asecond direction of extension, which second direction of extension isperpendicular to the first direction of extension and forms an obtuseangle to the front side of the second array 500 b. The use of the fourthelectromagnetic shield plate is optional.

By having the electromagnetic shield plates 520 and 521 between theradiating array 500 a and the receiving array 500 b, the amount of falsereflections from the radiating antenna 500 a reaching the receivingantenna 500 b is further reduced, thereby improving the signal to noiseratio.

FIG. 10 is a schematic cut through view of a radar system 600 holding asingle antenna module 510 as illustrated in FIG. 9 covered by aprotective radome 618 according to an example embodiment. The radome 618may be made of the same material as the radome 2118 of the antennasystem 2101 of FIG. 2a . The scanning radar system 2101 of FIG. 2a holdstwo back-to-back positioned antenna modules 2110 a and 2110 b, but it isalso within an embodiment to provide a detection system using a radarsystem having only a single antenna module 510, such as the radar system600 of FIG. 10. When using only a single radar module 510, the rotationspeed of the radar system 600 may be increased or doubled when comparedto the rotation speed of the radar system 2101 having two radar modules2110 a, 2110 b. When increasing the rotation speed, the exposure time onthe object target is decreased, thereby decreasing the signal to noiseratio.

It may therefore be preferred to use a radar system with two antennamodules as illustrated with the system 2101 of FIG. 2a . FIG. 11 is aschematic cut through view of an embodiment of a radar system 700holding two antenna modules 510 a and 510 b equal to the module 510 asillustrated in FIG. 9, and with both antenna modules 510 a, 510 bcovered by a protective radome 718. The radome 710 may be made of thesame material as the radome 2118 of the antenna system 2101 of FIG. 2 a.

The radome 618, 718 has a cylindrically shaped wall part surrounding theantenna module(s) 510 or 510 a and 510 a, and the wall part may beslightly inclined towards the antenna module(s) 510 or 510 a and 510 aforming a small acute inclination angle to a vertical axis of rotation,where this small acute angle should be no larger than 10°, such as nolarger than 5, such as about 3°. The radome 718 of FIG. 11 may in anexample embodiment be dimensioned with a height h1 of 561 mm, a lowerouter diameter Ø1 of 540 mm, and an upper outer diameter of Ø2 of 494mm, resulting in a small acute angle of about 3°. In an exampleembodiment the first and second shield plates 520, 521 of the radarantenna module 510 or modules 510 a and 510 b each have a second outeredge proximate the cylindrically wall part of the radome 618 or 718,said second outer edges being curve shaped to follow the interior of thecylindrically shaped radome 618 or 718. The third shield plate 522 of aradar antenna module 510 or 510 a and 510 b also has a second outer edgeproximate the cylindrically wall part of the radome 618 or 718, saidsecond outer edge also being curve shaped to follow the interior of thecylindrically shaped radome. The distance d1, see FIG. 11, between thesecond outer edge of the shield plates 520, 521 and 522 and the interiorof the cylindrically shaped wall part of the radome 618, 718 should beno larger than 15 mm, such as no larger than 10 mm, such as no largerthan 8 mm. The system 700 of FIG. 11 may in an example embodiment hold adistance d1 of about 8 mm. For the system 700 of FIG. 11, the first andsecond antenna modules 510 a and 510 b are arranged in a mirroredposition relative to a plane intersecting a vertical center axis ofrotation, see axis 2115 of FIG. 2 a.

FIG. 12 is a perspective view illustrating a radar system 800 with aback-to-back arrangement of two antenna modules 810 a and 810 b coveredby a radome 818 according to an example embodiment. Each of the modules810 a and 810 b are dimensioned similar to the module 510 of FIG. 9 andarranged in a mirrored position relative to a plane intersecting avertical center axis of rotation, see axis 2115 of FIG. 2a . Thus, thefirst antenna module 810 a holds a first and lower radiating array 800aa with four waveguide columns, and a second higher receiving array 800ba with eight waveguide columns. Both the first and second arrays 800 aaand 800 ba hold plate blinds arranged perpendicular to the longitudinaldirection of the waveguide columns, see FIG. 9. Similar to the firstantenna module 810 a, the second antenna module 810 b holds a first andlower radiating array 800 ab with four waveguide columns and a secondhigher receiving array 800 bb with eight waveguide columns, and both thefirst and second arrays 800 ab and 800 bb hold plate blinds arrangedperpendicular to the longitudinal direction of the waveguide columns,see FIG. 9.

For both the first and second antenna modules 810 a and 810 b, a firstelectromagnetic shield plate 820 a, 820 b and a second electromagneticshield plate 821 a, 821 b are positioned between the first radiatingarray 800 aa, 800 ab and the second receiving array 800 ba, 800 bb. Bothantenna modules 810 a and 810 b also hold a third electromagnetic shieldplate 822 a, 822 b positioned at a lower edge of the first radiatingarray 800 aa, 800 ab.

For both antenna modules 810 a, 810 b the first shield plate 820 a, 820b has a first outer edge in contact with an upper outermost arraysidewall of the first array 800 aa, 800 ab, the second shield plate 821a, 821 b has a first outer edge in contact with a lower outermost arraysidewall of the second array 800 ba, 800 bb, and the third shield plate822 a, 822 b has a first outer edge in contact with a lower outermostarray sidewall of the first array 800 aa, 800 ab. FIG. 12 shows how thefirst, second and third shield plates 820 a, 820 b, 821 a, 821 b and 822a, 822 b all have a second outer edge being curve shaped to follow theinterior of the cylindrically shaped radome 818. The radome 818 may bemade of the same material as the radome 2118 of the antenna system 2101of FIG. 2a and have the same outer dimensions as the radome 718 of thesystem 700 illustrated in FIG. 11. The distance d1, see FIG. 11, betweenthe second outer edge of the shield plates 820 a, 820 b, 821 a, 821 band 822 a, 822 b and the interior of the cylindrically shaped wall partof the radome 618 may also be equal to the distance d1 for the system700 of FIG. 11.

The first antenna module 810 a may also hold on-board circuitryincluding signal processing circuitry and electronic transmit circuitryand electronic receive circuitry, not shown in FIG. 12. The secondantenna module 810 b also holds on-board circuitry including signalgenerating system, not shown in FIG. 12, and electronic transmitcircuitry 823 b, and electronic receive circuitry 824 b. The system 800may be supported by a rotation system, not shown in FIG. 12, and holds amotor controller 819 for controlling the rotation system.

The following describes construction details for an example embodimentof the antenna array 200 of FIG. 3-6, and the first radiating arrays 300a, 500 a and the second receiving arrays 300 b, 500 b of the antennamodules 310, 501 of FIGS. 7 and 9, respectively, when designed tooperate in a wideband frequency range of 9550 to 9750 MHz, correspondingto a free-space wavelength λ₀ in the range of 30.77-31.4 mm, or tooperate with a free-space wavelength λ₀ about 30 mm.

In order to operate in the above-mentioned frequency range, thewaveguide columns 203, 303 a, 503 a, 303 b, 503 b are dimensioned withan internal height “a” of the wide inner surfaces to be about ⅔ λ₀, andset to 20 mm, and an internal width “b” of the narrow inner back andfront surfaces to be about ⅓ λ₀, and set to 10 mm. The waveguide columns203 are produced by use of milling from the first and second metalelements 201, 202 being of anodized aluminium having a plate thicknessof 12 mm, and the thickness of the walls 106, 107 defining the upperparts of the wide inner surfaces of the waveguide columns 103 b, 103 isabout 2 mm, and the thickness of the narrow front wall is also 2 mm.

The guided wavelength, λ_(g), can be calculated from the values of λ₀and “a”, where λ₀ set to 30.77 mm gives a value of λ_(g), which is equalto 48 mm, and where λ₀ set to 31.4 mm gives a value of λ_(g), which isequal to 50.64 mm.

From the above values of λ₀ and λ_(g), the average values are found asλ_(0,av) equal to 31 mm and λ_(g,av) equal to 49.3 mm, which gives avalue for half the free-space wavelength, ½ λ₀, to be about 15.5 mm, anda value for half the guided wavelength, ½ λ_(g), to be about 24.66 mm.

The distance between the centres of neighbouring slots 208 of awaveguide column 203, 303 a, 303 b, 503 a, 503 b is set to 25 mm, equalto about half the guided wavelength, ½ λ_(g), and the total length ofthe edge-slots 208 including the penetrations into the sidewalls 206,207 is set to about 15 mm, equal to about half the free-spacewavelength, ½ λ₀. The width of the edge-slots 208 is set to 3.6 mm, andthe slots 208 are arranged with an angular displacement of about 35degrees to the longitudinal direction to the waveguide column 203, whereneighbouring slots 208 are arranged with equal, but opposite angulardisplacement.

For the travelling waveguide columns 203, 303 a, 303 b, 503 a, 503 b theabsorbing load at the second end is arranged with a spacing of threequarters of the guided wavelength, λ_(g), which is equal to 37 mm, tothe centre of the last slot 208. The signal probe 214 is inserted intothe column 203 with a spacing of three quarters of a guided wavelength,λ_(g), which is about 42 mm, to the centre of the first slot 208, whilethe short circuiting end geometry at the first end is arranged with aspacing of one quarter of the guided wavelength, λ_(g), which is atleast about 12.4 mm, to the centre of the coupling probe 214.

The distance between the centres of adjacent positioned waveguidescolumns 203, 303 a, 303 b, 503 a, 503 b is set to be 20 mm, which isabout two third of the free-space wavelength λ₀. This distance leaves afree space of about 6 mm between the sidewalls of neighbouring columns203, 303 a, 303 b.

The spacing between the centres of adjacent plate blinds 212, 312 a, 312b, 512 a, 512 b is set equal to the distance between the centres ofneighbouring slots 208, which is 25 mm, to be about half the guidedsignal wavelength, λ_(g), and the distance between the first and secondouter surfaces of the plate blinds 212, 312 a, 312 b, 5012 a, 512 b maybe set to 9.86-12 mm, which is in between one third and half of thefree-space signal wave length, λ₀. The spacing left between oppositeouter surfaces of neighbouring plate blinds 212, 312 a, 312 b, 512 a,512 b is then about 12.66-14.8 mm, which is below half the free-spacesignal wave length of 15.5 mm, in order to effectively reduce thecross-polarization radiation. The height of the parallel outer surfacesof the plate blinds 212, 312 a, 312 b, 512 a, 512 b above the outerfront surface of the columns 203, 303 a, 303 b, 503 a, 503 b may be setto be 15.5 mm, which is substantial equal to ½ of the free-space signalwave length, to thereby further reduce the cross-polarization radiation.The U-shaped plate blinds 212, 312 a, 312 b, 512 a, 512 b are made inaluminium with a sidewall thickness of 1.8 mm. The bottom part of theU-shaped plate blinds 212, 312, 512 has a wall thickness of 1.7 mm, andholds the tail of the dovetail joint to fit with the socket of thedovetail joint formed in part of the waveguide columns 203, 303 a, 303b, 503 a, 503 b.

The total length of the arrays 300 a, 300 b, 500 a, 500 b and thecolumns 303 a, 303 b, 503 a, 503 b is 414 mm, and for the module 510 ofFIG. 9 the total width of the first array 500 a is 105 mm while thetotal width of the second array 500 b is 185 mm. The length of the plateblinds 312 a, 512 a covering the four columns 303 a, 503 a of theradiating array 300 a, 500 a is 80 mm, and the length of the plateblinds 312 b, 512 b covering the eight columns 303 b, 503 b of thereceiving array 300 b, 503 b is 160 mm. The distance between closestside walls of neighboring plate blinds 312 a, 312 b, 512 a, 512 b is14.5 mm, and the distance between the first and second outer surfaces ofthe plate blinds 312 a, 312 b, 512 a, 512 b is set to 11.5 mm.

Further measures indicating the positioning of the first radiating array500 a and the second receiving array 500 b according to an embodiment ofthe antenna module 510 of FIG. 9 are given below with reference to FIG.13.

In FIG. 13, L1 indicates the perpendicular array distance, which is setto 75 mm, equal to 7.5 times the internal width of the waveguide columns503 a, 503 b; L2 indicates the parallel column distance, which is set to197 mm, equal to 19.7 times the internal width of the waveguide columns503 a, 503 b; L3 indicates the parallel array distance, which is set to172 mm; L4 indicates the total width of the first array 500 a set to 105mm; L5 indicates the total width of the second array 500 b set to 185mm; L6 indicates the distance from the outer sidewall of the outermostupper waveguide column of the first array 500 a to the contact pointbetween the first shield plate 520 and the second shield plates 521,which is set to 120 mm; L7 indicates the distance from the outersidewall of the outermost lower waveguide column of the second array 500b to the contact point between the second shield plate 521 and the firstshield plates 520, which is set to 77 mm; L8 indicates the distance fromthe outer sidewall of the outermost lower waveguide column of the firstarray 500 a to the outermost part of the curved third shield plate 522,which is set to 71 mm; L9 indicates the distance from a lower upper edgeof the plate blinds 512 a of the first array 500 a to the bottom of thesupport 529, which is set to 59 mm; L10 indicates the distance from alower upper edge of the plate blinds 512 b of the second array 500 b tothe bottom of the support 529, which is set to 345 mm, where the bottomof the support may be equal to a top part of a rotation system, to whichthe antenna module 510 may be secured.

In FIG. 13, α1 indicates the first obtuse angle from the seconddirection of extension along the front side of the first shield plate520 to the front side of the first array 500 a, which first obtuse angleis set to 120°; α2 indicates the second obtuse angle from the seconddirection of extension along the front side of the second shield plate521 to the front side of the second array 500 b, which second obtuse isset to 120°; α3 indicates the third obtuse angle from the seconddirection of extension along the front side of the third shield plate522 to the front side of the first array 500 a, which third obtuse angleis set to 120°; α4 indicates the first acute angle being formed betweenthe second direction of extension of the first shield plate 520 and thesecond direction of extension of the second shield plate 521, whichfirst acute angle is set to 60°.

When an antenna modules 510 is supported by a rotation system forrotating the antenna module around a vertical axis, such as the rotationsystem 2116 of FIG. 2a the antenna module 510 is secured to the rotationsystem with the first and second planar antenna arrays 500 a and 500 bpositioned with the first and second planes holding a second acute angleα5 to the vertical axis of rotation, which second acute angle α5 may bein the range of 15° to 25°. For the embodiment illustrated in FIG. 13,the second acute angle α5 is set to 20°.

It is noted that for the radar system 800 of FIG. 12, each of themodules 810 a and 810 b may be dimensioned according to the measuresgiven above for the module 510 of FIG. 9 and further indicated withreference to FIG. 13. Thus, both antenna modules 810 a and 810 b may besupported by a rotation system with the first and second planar antennaarrays 800 aa, 800 ab and 800 ba, 800 bb positioned with the first andsecond planes holding a second acute angle α5 of 20° to the verticalaxis of rotation.

FIGS. 14a-14c illustrate scanning of a fixed object A, 105 a, using aradar system holding two back-to-back antenna modules, such as the radarsystem 101 of FIG. 1a with antenna module 110 a, 110 b, according to anexample embodiment. The difference in azimuth angles between the twomodules 110 a and 110 b is 180°. In FIG. 14a , the azimuth angle is 0°,180° and the object A is scanned by radiated waves 113 a of the firstantenna module 110 a, while no object is scanned by the waves 113 b ofthe second module 110 b. In FIG. 14b , the azimuth angle is 90°, 270°and no object is scanned. In FIG. 14c , the azimuth angle is 180°, 0°and the object A is scanned by radiated waves 113 b of the secondantenna module 110 b, while no object is scanned by the waves 113 a ofthe first module 110 a.

FIGS. 15a-15i illustrate scanning of four moving objects A,B,C,D, 105a,b,c,d, using a radar system, such as the system 101, holding twoback-to-back antenna modules 110 a, 110 b according to an exampleembodiment. In FIG. 15a , the azimuth angle is 0°, 180° and no objectsare scanned. In FIG. 15b , the azimuth angle is 45°, 225° and object Ais scanned by radiated waves 113 a of the first antenna module 110 a,while no object is scanned by the waves 113 b of the second module 110b. In FIG. 15c , the azimuth angle is 90°, 270° and object C is scannedby radiated waves 113 b of the second antenna module 110 b, while noobject is scanned by the waves 113 a of the first module 110 a. In FIG.15d , the azimuth angle is 135°, 305° and object B is scanned byradiated waves 113 a of the first antenna module 110 a, and object D isscanned by radiated waves 113 b of the second antenna module 110 b. InFIG. 15e , the azimuth angle is 180°, 0° and no objects are scanned. InFIG. 15f , the azimuth angle is 225°, 45° and object C is scanned byradiated waves 113 a of the first antenna module 110 a, while no objectis scanned by the waves 113 b of the second module 110 b. In FIG. 15g ,the azimuth angle is 270°, 90° and object D is scanned by radiated waves113 a of the first antenna module 110 a, and object A is scanned byradiated waves 113 b of the second antenna module 110 b. In FIG. 15h ,the azimuth angle is 315°, 135° and object B is scanned by radiatedwaves 113 b of the second antenna module 110 b, while no object isscanned by the waves 113 a of the first module 110 a. In FIG. 15i , theazimuth angle is 360°, 0° and object C is scanned by radiated waves 113b of the second antenna module 110 b, while no object is scanned by thewaves 113 a of the first module 110 a.

FIG. 16 is a table, Table I, giving an overview of the scanning resultsillustrated in FIGS. 15a-15i . Table I shows which objects are being hitor scanned with progress in time of rotation of the radar system 101,which of the antenna modules 110 a or 110 b hits or scans the object andat which azimuth angle. Table I also indicates a change in range of themoving objects from one scan to a following scan, where a first range isindicated by Y, a second range is Y+δ, and a third range is Y+δ2.

FIG. 17 illustrates simultaneous radar image capture for two opposedradar image lines using a radar system, such as the system 101, holdingtwo back-to-back antenna modules 110 a and 110 b according to an exampleembodiment. A full circular radar has 80 image lines to cover a full360° radar image, whereby each image line covers 4.5°. By having the twoback-to-back arranged antenna modules 110 a and 110 b, two oppositeradar image lines are scanned at the same time. Thus, when the radarsystem 101 rotates with 30 rounds per minute, RPM, one full radar imagecan be obtained for half a rotation and for every second. The radarmodules 110 a and 110 b may be configured to have an azimuth beam widthof 6° in order to obtain a satisfying radar signal exposure time foreach image line of 4.5°. Each image line may be divided inn 1587 rangecells, and each radar antenna module 110 a and 110 b may be configuredto transmit 100 FMCW sweeps per image line, to thereby obtain thenecessary data for generating radar plots.

The present disclosure has been described in conjunction with variousembodiments herein. However, other variations to the disclosedembodiments can be understood and effected by those skilled in the artin practicing the claimed present disclosure, from a study of thedrawings, the disclosure, and the appended claims. In the claims, theword “comprising” does not exclude other elements or steps, and theindefinite article “a” or “an” does not exclude a plurality.

1-40. (canceled)
 41. A radar system comprising a first and a secondantenna module, each said antenna module comprising: a first planarslotted waveguide antenna array configured for radiating electromagneticwaves; and a second planar slotted waveguide antenna array configuredfor receiving electromagnetic waves; wherein for each of the antennamodules, each planar slotted waveguide antenna array comprises severallongitudinal extending waveguide columns disposed in a parallel andadjacent position with respect to one another, said waveguide columnshaving a front side and a rear side with a plurality of cavity slots onthe front side, and said waveguide columns further having first andsecond column ends; and wherein for each of the antenna modules, thefirst and second antenna arrays are arranged with the longitudinaldirection of the waveguide columns extending in a single, horizontaldirection, and with the waveguide columns of the first antenna arraydisposed in a parallel position to the waveguide columns of the secondantenna array; said radar system further comprising a rotation systemconfigured for supporting and rotating the first and second antennamodules around a vertical axis, with the first and second antennamodules arranged in a back-to-back position on opposite sides of a planeintersecting the vertical axis of rotation, and with the rear side ofthe waveguide columns of the antenna arrays of the first antenna modulefacing the rear side of the waveguide columns of the antenna arrays ofthe second antenna module; characterized in that for each antennamodule, the waveguide columns of the first antenna array are disposedbelow the waveguide columns of the second antenna array when compared tothe vertical axis of rotation; and in that for each antenna module, anelectromagnetic shield or shield plate is arranged substantiallyparallel to the waveguide columns and between the first lower radiatingantenna array and the second upper receiving antenna array, said shieldor shield plate extending outwards from the front side of the antennamodule.
 42. A radar system according to claims 41, wherein the cavityslots on the front side of the columns of the second antenna array ofthe first antenna module are arranged in a partially upwards facingplane having a first acute angle to the vertical direction, and whereinthe cavity slots on the front side of the columns of the first antennaarray of the second module are arranged in a partially upwards facingplane having a second acute angle to the vertical direction.
 43. A radarsystem according to claim 42, wherein the first acute angle issubstantial equal to the second acute angle, and wherein said first andsecond acute angles preferably are in the range of 10-30°, such as about20°.
 44. A radar system according to claim 41, wherein the first andsecond antenna modules are arranged in a mirrored position relative tosaid plane intersecting the vertical axis of rotation.
 45. A radarsystem according to claim 41, wherein the waveguide columns within thefirst and second antenna arrays of both the first and second antennamodule have equal dimensions; and wherein for each of the antennamodules, the front side of the columns holding the cavity slots of boththe first and second antenna arrays are positioned substantially in thesame plane.
 46. A radar system according to claim 41, said systemfurther comprising a protective housing in the form of a radome coveringsaid first and second antenna modules.
 47. A radar system according toclaim 46, wherein the radome is made of a material having a highelectromagnetic transparency, such as made of a polyethylene (PE) orpolypropylene (PP) based ultra heigh molecular weight plastic material;and wherein the radome preferably is made of a material having athickness in the range of 1-3 mm, such as in the range of 1-2 mm or suchas in the range of 1-1.5 mm.
 48. A radar system according to claim 41,wherein for each antenna module, a lower electromagnetic shield orshield plate is arranged substantially parallel to the waveguide columnsand below the lowermost waveguide column of the first lower radiatingantenna array, said lower electromagnetic shield or shield plateextending outwards from the front side of the antenna module.
 49. Aradar system according to claim 41, wherein for each antenna module, anupper electromagnetic shield or shield plate is arranged substantiallyparallel to the waveguide columns and above the uppermost waveguidecolumn of the second upper receiving antenna array, said upperelectromagnetic shield or shield plate extending outwards from the frontside of the antenna module.
 50. A radar system according to claim 41,wherein for each antenna module, the first antenna array holds a numberof parallel plate blinds secured to the front side of the first antennaarray besides or between the cavity slots and substantiallyperpendicular to the longitudinal direction of the waveguide columns ofthe first antenna array; and wherein the second antenna array holds anumber of parallel plate blinds secured to the front side of the secondantenna array besides or between the cavity slots and substantiallyperpendicular to the longitudinal direction of the waveguide columns ofthe second antenna array.
 51. A radar system according to claim 41,wherein for each of the antenna module, the number of waveguide columnsin the second receiving array is larger than the number of waveguidecolumns in the first radiating array; and wherein for each antennamodule, the number of waveguide columns in the second receiving array ispreferably twice the number of waveguide columns in the first radiatingarray.
 52. A radar system according to claim 41, wherein the systemfurther comprises a signal generating system holding a single signalgenerator, and wherein the first antenna module holds first electronictransmit circuitry configured for feeding the first radiating array ofthe first antenna module to radiate first electromagnetic signals, andthe second antenna module holds second electronic transmit circuitryconfigured for feeding the first radiating array of the second antennamodule to radiate second electromagnetic signals, said first and secondelectromagnetic signals being fully synchronized electromagnetic signalsbased at least partly on signals provided by said single signalgenerator.
 53. A radar system according to claim 52, wherein the firstantenna module holds first electronic receive circuitry configured forprocessing signals received by the second receiving array of the firstantenna module, and the second antenna module holds second electronicreceive circuitry configured for processing signals received by thesecond receiving array of the second antenna module, said first andsecond electronic receive circuitry being configured for processing thereceived signals in synchronization with the radiated electromagneticsignals, said synchronization being based on signals provided by thesingle signal generator.
 54. A radar system according to claim 41,wherein the system further comprises: first processing circuitry forprocessing signals received by the first antenna module, said firstprocessing circuitry being configured to provide first type radar plotsof detected objects presented by said signals received by the firstantenna module; and second processing circuitry for processing signalsreceived by the second antenna module, said second processing circuitrybeing configured to provide second type radar plots of detected objectspresented by said signals received by the second antenna module;
 55. Aradar system according to claim 54, wherein the system furthercomprises: third processing circuitry being radar track processingcircuitry, said radar track processing circuitry being configured toprovide a radar track for a detected object based on both first andsecond type radar plots.
 56. A radar system comprising a first radarantenna module comprising: a first planar slotted waveguide antennaarray configured for radiating electromagnetic waves, and a secondplanar slotted waveguide antenna array configured for receivingelectromagnetic waves, wherein: each planar slotted waveguide antennaarray comprises several longitudinal extending waveguide columnsdisposed in a parallel and adjacent position with respect to oneanother, said waveguide columns having a front side and a rear side witha plurality of cavity slots on the front side, and said waveguidecolumns further having first and second column ends; the waveguidecolumns of the first and second antenna arrays have equal internalheight and equal internal width; the first and second antenna arrays arearranged with the waveguide columns of the first antenna array disposedin a parallel position to the waveguide columns of the second antennaarray; the front side of the columns holding the cavity slots of thefirst planar antenna array are positioned in a first plane and the frontside of the columns holding the cavity slots of the second planarantenna array are positioned in a second plane parallel to said firstplane; and the first and second antenna arrays are positioned at adistance to each other with a longitudinal extending outer sidewall ofan outermost waveguide column of the first array arranged closest to alongitudinal extending outer sidewall of an outermost waveguide columnof the second array, said closest outer sidewalls of the outermostcolumns of the first and second antenna arrays positioned with a minimumparallel column distance to each other in a direction parallel to thefirst and second planes, said minimum parallel column distance being atleast 10 times the internal width of the waveguide columns.
 57. A radarsystem according to claim 56, wherein said minimum parallel columndistance is at least 12 times or at least 15 times the internal width ofthe waveguide columns.
 58. A radar system according to claim 56, whereinthe first and second parallel planes are offset with a minimumperpendicular array distance to each other in a direction perpendicularto said planes, said minimum perpendicular array distance being at least3 times or at least 5 times the internal width of said waveguidecolumns; wherein the front sides of the first and second antenna arraysface the same direction being a front direction of the antenna module;and wherein the first plane is offset from the second plane by saidperpendicular array distance in a direction opposite to said frontdirection.
 59. A radar system according to claim 56, wherein the firstantenna array has a first longitudinal extending outermost arraysidewall closest to a second longitudinal extending outermost arraysidewall of the second antenna array, said closest first and secondoutermost array sidewalls positioned with a minimum parallel arraydistance to each other in a direction parallel to the first and secondplanes, said minimum parallel array distance being smaller than or equalto the minimum parallel column distance.
 60. A radar system according toclaim 59, wherein one or more electromagnetic shield(s) is/are arrangedbetween the first radiating antenna array and the second receivingantenna array; wherein the front sides of the first and second antennaarrays face the same direction being a front direction of the antennamodule; and wherein at least a part of the electromagnetic shieldsextends outwards from the front side of the antenna module.
 61. A radarsystem according to claim 59, wherein one or more electromagneticshield(s) is/are arranged between the first radiating antenna array andthe second receiving antenna array; wherein the front sides of the firstand second antenna arrays face the same direction being a frontdirection of the antenna module; and wherein at least a part of theelectromagnetic shields extends outwards from the front side of theantenna module; wherein the one or more electromagnetic shields comprisea first shield plate and a second shield plate with both shield plateshaving a first direction of extension and a second direction ofextension perpendicular to the first direction of extension, with thefirst direction of extension for both shield plates being parallel tothe longitudinal extension of the waveguides; wherein the first shieldplate has a first outer edge in contact with said first outermost arraysidewall of the first array and the second shield plate has a firstouter edge in contact with said second outermost array sidewall of thesecond array; and wherein the second direction of extension of the firstshield plate has a first obtuse angle to the front side of the firstarray and the second direction of extension of the second shield platehas a second obtuse angle to the front side of the second array.
 62. Aradar system according to claim 61, wherein the second direction ofextension of the first shield plate differs from the second direction ofextension of the second shield plate, and wherein the second directionof extension of the first shield plate forms a first acute angle to thesecond direction of extension of the second shield plate.
 63. A radarsystem according to claim 60, wherein the first antenna array has asecond longitudinal extending outer array sidewall opposite to saidfirst outer array sidewall, and wherein a third shield plate is arrangedin contact with said second longitudinal extending outer array sidewallof the first array, said third shield plate extending outwards from thefront side of the first antenna array; wherein the third shield platehas a first and a second direction of extension, with the firstdirection of extension of the third shield plate being parallel to thelongitudinal extension of the waveguides; and wherein the seconddirection of extension of the third shield plate differs from the seconddirection of extension of the first shield plate, with the seconddirection of extension of the third shield plate having a third obtuseangle to the front side of the first array.
 64. A radar system accordingto claim 66, said system further comprising a rotation system configuredfor supporting and rotating the first antenna module around a verticalaxis, wherein the first radar antenna module is secured to the rotationsystem with the first and second planar antenna arrays positioned withthe first and second planes holding a second acute angle to the verticalaxis of rotation.
 65. A radar system according to claim 64, said systemfurther comprising a second radar antenna module being configured anddimensioned equal to the first radar antenna module, said second radarantenna module being supported by the rotation system with the first andsecond antenna modules arranged in a back-to-back position on oppositesides of a plane intersecting the axis of rotation, with the rear sideof the waveguide columns of the antenna arrays of the first antennamodule facing the rear side of the waveguide columns of the antennaarrays of the second antenna module; and wherein the second radarantenna module is secured to the rotation system with its first andsecond planar antenna arrays positioned with the first and second planesholding said second acute angle to the vertical axis of rotation.
 66. Aradar system according to claim 61, said system further comprising arotation system configured for supporting and rotating the first antennamodule around a vertical axis, wherein the first radar antenna module issecured to the rotation system with the first and second planar antennaarrays positioned with the first and second planes holding a secondacute angle to the vertical axis of rotation; and said system furthercomprising a protective housing in the form of a radome covering saidantenna module(s); wherein the radome has a cylindrically shaped wallpart surrounding the antenna module(s), said wall part being slightlyinclined towards the antenna module(s) forming a small acute inclinationangle to said axis of rotation, said small acute angle being no largerthan 10°, such as no larger than 5, such as about 3°; and wherein thefirst and second shield plates of a radar antenna module each have asecond outer edge proximate the cylindrically wall part of the radome,said second outer edges being curve shaped to follow the interior of thecylindrically shaped radome.
 67. A radar system according to claim 63said system further comprising a rotation system configured forsupporting and rotating the first antenna module around a vertical axis,wherein the first radar antenna module is secured to the rotation systemwith the first and second planar antenna arrays positioned with thefirst and second planes holding a second acute angle to the verticalaxis of rotation; and said system further comprising a protectivehousing in the form of a radome covering said antenna module(s); whereinthe radome has a cylindrically shaped wall part surrounding the antennamodule(s), said wall part being slightly inclined towards the antennamodule(s) forming a small acute inclination angle to said axis ofrotation, said small acute angle being no larger than 10°, such as nolarger than 5, such as about 3°; wherein the first and second shieldplates of a radar antenna module each have a second outer edge proximatethe cylindrically wall part of the radome, said second outer edges beingcurve shaped to follow the interior of the cylindrically shaped radome;and wherein the third shield plate of a radar antenna module has asecond outer edge proximate the cylindrically wall part of the radome,said second outer edge being curve shaped to follow the interior of thecylindrically shaped radome.
 68. A radar system comprising a first radarantenna module comprising: a first planar slotted waveguide antennaarray configured for radiating electromagnetic waves, and a secondplanar slotted waveguide antenna array configured for receivingelectromagnetic waves, wherein: each planar slotted waveguide antennaarray comprises several longitudinal extending waveguide columnsdisposed in a parallel and adjacent position with respect to oneanother, said waveguide columns having a front side and a rear side witha plurality of cavity slots on the front side, and said waveguidecolumns further having first and second column ends; the waveguidecolumns of the first and second antenna arrays have equal internalheight and equal internal width; the first and second antenna arrays arearranged with the waveguide columns of the first antenna array disposedin a parallel position to the waveguide columns of the second antennaarray; the front side of the columns holding the cavity slots of thefirst planar antenna array are positioned in a first plane and the frontside of the columns holding the cavity slots of the second planarantenna array are positioned in a second plane parallel to said firstplane; and the first and second parallel planes are offset with aminimum perpendicular array distance to each other in a directionperpendicular to said planes.
 69. A radar system according to claim 68,wherein said minimum perpendicular array distance is at least 3 times orat least 5 times the internal width of said waveguide columns.
 70. Aradar system according to claim 68, wherein the front sides of the firstand second antenna arrays face the same direction being a frontdirection of the antenna module; and wherein the first plane is offsetfrom the second plane by said perpendicular array distance in adirection opposite to said front direction.
 71. A radar system accordingto claim 68, wherein the first antenna and second antenna arrays arepositioned at a distance to each other with a longitudinal extendingouter sidewall of an outermost waveguide column of the first arrayarranged closest to a longitudinal extending outer sidewall of anoutermost waveguide column of the second array, said closest outersidewalls of the outermost columns of the first and second antennaarrays positioned with a minimum parallel column distance to each otherin a direction parallel to the first and second planes, said minimumparallel column distance being at least 2 times the internal width ofthe waveguide columns, such as at least 3 times, such as at least 5times, such as at least 10 times, such as at 12 times or at least 15times the internal width of the waveguide columns.
 72. A radar systemaccording to claim 71, wherein the first antenna array has a firstlongitudinal extending outermost array sidewall closest to a secondlongitudinal extending outermost array sidewall of the second antennaarray, said closest first and second outermost array sidewallspositioned with a minimum parallel array distance to each other in adirection parallel to the first and second planes, said minimum parallelarray distance being smaller than or equal to the minimum parallelcolumn distance.
 73. A radar system according to claim 68, wherein oneor more electromagnetic shield(s) is/are arranged between the firstradiating antenna array and the second receiving antenna array; whereinthe front sides of the first and second antenna arrays face the samedirection being a front direction of the antenna module; and wherein atleast a part of the electromagnetic shields extends outwards from thefront side of the antenna module.
 74. A radar system according to claim72, wherein one or more electromagnetic shield(s) is/are arrangedbetween the first radiating antenna array and the second receivingantenna array; wherein the front sides of the first and second antennaarrays face the same direction being a front direction of the antennamodule; wherein at least a part of the electromagnetic shields extendsoutwards from the front side of the antenna module; wherein the one ormore electromagnetic shields comprise a first shield plate and a secondshield plate with both shield plates having a first direction ofextension and a second direction of extension perpendicular to the firstdirection of extension, and wherein the first direction of extension forboth shield plates is parallel to the longitudinal extension of thewaveguides; wherein the first shield plate has a first outer edge incontact with said first outermost array sidewall of the first array andthe second shield plate has a first outer edge in contact with saidsecond outermost array sidewall of the second array; and wherein thesecond direction of extension of the first shield plate has a firstobtuse angle to the front side of the first array and the seconddirection of extension of the second shield plate has a second obtuseangle to the front side of the second array.
 75. A radar systemaccording to claim 74, wherein the second direction of extension of thefirst shield plate differs from the second direction of extension of thesecond shield plate, and wherein the second direction of extension ofthe first shield plate forms a first acute angle to the second directionof extension of the second shield plate.
 76. A radar system according toclaim 74, wherein the first antenna array has a second longitudinalextending outer array sidewall opposite to said first outer arraysidewall, and wherein a third shield plate is arranged in contact withsaid second longitudinal extending outer array sidewall of the firstarray, said third shield plate extending outwards from the front side ofthe first antenna array; wherein the third shield plate has a first anda second direction of extension, and wherein the first direction ofextension of the third shield plate is parallel to the longitudinalextension of the waveguides; and wherein the second direction ofextension of the third shield plate differs from the second direction ofextension of the first shield plate, and wherein the second direction ofextension of the third shield plate has a third obtuse angle to thefront side of the first array.
 77. A radar system according to claim 78,said system further comprising a rotation system configured forsupporting and rotating the first antenna module around a vertical axis,wherein the first radar antenna module is secured to the rotation systemwith the first and second planar antenna arrays positioned with thefirst and second planes holding a second acute angle to the verticalaxis of rotation.
 78. A radar system according to claim 77, said systemfurther comprising a second radar antenna module being configured anddimensioned equal to the first radar antenna module, said second radarantenna module being supported by the rotation system with the first andsecond antenna modules arranged in a back-to-back position on oppositesides of a plane intersecting the axis of rotation, with the rear sideof the waveguide columns of the antenna arrays of the first antennamodule facing the rear side of the waveguide columns of the antennaarrays of the second antenna module; and wherein the second radarantenna module is secured to the rotation system with its first andsecond planar antenna arrays positioned with the first and second planesholding said second acute angle to the vertical axis of rotation.
 79. Aradar system according to claim 74, said system further comprising arotation system configured for supporting and rotating the first antennamodule around a vertical axis, wherein the first radar antenna module issecured to the rotation system with the first and second planar antennaarrays positioned with the first and second planes holding a secondacute angle to the vertical axis of rotation; and said system furthercomprising a protective housing in the form of a radome covering saidantenna module(s); wherein the radome has a cylindrically shaped wallpart surrounding the antenna module(s), said wall part being slightlyinclined towards the antenna module(s) forming a small acute inclinationangle to said axis of rotation, said small acute angle being no largerthan 10°, such as no larger than 5, such as about 3°; and wherein thefirst and second shield plates of a radar antenna module each have asecond outer edge proximate the cylindrically wall part of the radome,said second outer edges being curve shaped to follow the interior of thecylindrically shaped radome.
 80. A radar system according to claim 76,said system further comprising a rotation system configured forsupporting and rotating the first antenna module around a vertical axis,wherein the first radar antenna module is secured to the rotation systemwith the first and second planar antenna arrays positioned with thefirst and second planes holding a second acute angle to the verticalaxis of rotation; and said system further comprising a protectivehousing in the form of a radome covering said antenna module(s); whereinthe radome has a cylindrically shaped wall part surrounding the antennamodule(s), said wall part being slightly inclined towards the antennamodule(s) forming a small acute inclination angle to said axis ofrotation, said small acute angle being no larger than 10° , such as nolarger than 5, such as about 3° ; wherein the first and second shieldplates of a radar antenna module each have a second outer edge proximatethe cylindrically wall part of the radome, said second outer edges beingcurve shaped to follow the interior of the cylindrically shaped radome;and wherein the third shield plate of a radar antenna module has asecond outer edge proximate the cylindrically wall part of the radome,said second outer edge being curve shaped to follow the interior of thecylindrically shaped radome.